So I went to look at a car today. 82 SD with 227k. Interior is pretty good, intact blue MB Tex, good to very good wood. The original Becker tape deck works fine, speakers sound reasonably good. All dash lights function. White paint nice and shiny, grill and bumpers nice. Car drives very well with some exceptions which I'll explain below. I'm an Arizona native and this is not an AZ car. I'm not used to having to look for rust. There was some very minimal bubbling at the wheel wells. Looked like a pretty easy fix. Flashlight inspection didn't show any obvious rust, but like I say, I'm not used to having to look for rust.
The car ran well as far as I could tell, but I can't believe how ignorant I felt driving it. I've driven a total of 3 so far. Tracked straight, steering seemed tight, braking straight and uneventful. These are the deficits that stood out, in order from least important to most worrisome:

The sunroof works, but has to be closed from the outside due to some sort of loose trim piece that won't go into place without help. No big deal. Sunroofs are a dumb idea in the desert anyway. If it's warm enough to open the SR, it's AC time, IMO.
Climate control worked, but was wimpy IMO. Converted to 134a or whatever you call it.
The rear windows showed some clouding at the lower corners which if I've read correctly here is indicative of water leakage. I could find no rust or staining in the trunk or on the package tray inside.
The driver's seat is sprung, big time. Saggy and lumpy. This would be a deal breaker for me, but my son is going to drive it so it may not matter. I'm betting finding a replacement seat will be an expensive pain in the arse.

The vehicle leaks oil. I've heard people say "it's a diesel, it leaks some" and I've heard others say that's not true with proper maint. After a long drive, I let the car sit for 10 minutes running while I looked at other stuff. There was probably 2 tablespoons of oil under it afterwards.
I pulled the dipstick. The oil was coal, charcoal briquette, old cast iron skillet black. Guy says "it's due for an oil change". I don't believe I have EVER seen oil this color. Not Hershey's syrup blown head gasket brown, coal effing black. Is that normal?? The coolant overflow tank looked fine and didn't smell of oil. My ancient Ford 351 Cleveland ranch truck gets it's oil changed maybe once a year and the oil is never that color.
There seemed to be a film of fuel on top of the fuel filter canister. Seeping fuel from the lines or just a sloppy change? Couldn't tell...
I've read here that a crisp shifting transmission is best, but the car's shift out of low was way harder than crisp. Once it seemed to stumble a bit or tried to shift out of low too soon maybe. Higher gear shifts seemed OK.

Unfortunately this car isn't where I can take it to a mechanic who knows merc's. It's 75 miles away from me and it's the guy's daily driver. I know he's asking way too much at 3400. I've already decided if I can get some assurance about these other concerns I'll only pay maybe 1800 tops.
Your comments will be greatly appreciated. Thanks!

You said you're an AZ native? Is the car in AZ?

If so I could help you look it over. (I'm an ASE master certified tech by trade and a multiple Benz turbodiesel owner as seen in sig) Especially if it's in Phoenix area- that would be easy.

As for your questions: The oil is supposed to be black (my 300SD would turn it black within 10 minutes of the oil change)- the soot in diesel combustion, for lack of a more technical explanation, colors the oil.

It's not supposed to leak seriously though. A little seepage is normal, but my SD leaked seriously, and it also lacked power (I believe blow-by was pressurizing the crankcase beyond what the ventilation system could handle in my case) whereas my 300TD has no leaks to speak of and whistles along at 85-90 mph with ease.

I'll let others jump in as regards the other questions but it sounds like this car may be a little tired. Just my off-the-cuff answer...

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1985 300TD
1984 380SL
1983 280SE (full Euro, trunk triangle and all!)

Formerly owned:
1986 420SEL
1984 300D
1983 300D
1981 300SD
1976 300D

Soot black oil is normal. Drive around the block after an oil change and it'll get that black.

These systems aren't optimized for R134a. If you know your way around AC systems, you can probably revert to R12. Otherwise I'd hold out and even pay more for a car with suitable AC.

I'm rust ignorant like you but I'd pay close attention to the junction of glass, trim and body along the forward edge of the trunk lid. Once the seal gives, you'll have puddles in the pocket behind the rear wheel then puddles in the rear floor.

I don't know about glass fogging from water leaks. I know the glass they use in these cars can delaminate and there's nothing you can do about it other than replace the gla$$.

It's not difficult to tune transmission shifts but hopefully it's in fair shape that tuning will net a long term benefit. I'd go by the condition of the fluid. Wipe the dipstick on a white lintfree cloth and see if there's anything but red fluid. I'll accept a trace of silt.

2 tablespoons after a test drive is unacceptable. It might be easy to fix but that's a lot in relative terms. I've had engines with not a dry spot on the underside yet nothing makes it to my driveway.

Sixto
87 300D

Thanks! I feel better about the oil and sorta had the idea that the color might be normal. I'd love to take somebody with me to see it again, but it's outside Phoenix, up in Groom Creek near Prescott. The guy is a Sheriff and works goofy shifts. I'm retired and could meet somebody over there almost anytime. I'm in Cornville, between Sedona and Cottonwood. We have a great shop in Sedona, but they're so busy it's hard to schedule a PPI with them, not to mention pricey. Can't possibly pay a hundred bucks for every one I look at...It sure seemed to me like a lot of oil on the ground in only a few minutes.
I'm going to post a few pics in a while, but I don't think my wife got any under hood shots. Is it a big deal to revert back to Freon on the AC?

Oil leak may be something simple, maybe not. You'll need to determine with a close inspection. (color, normal)
Minor paint bubbling, not a big issue. Check the floor, under mats inside and frame outside.
More than likely a spring or two have broken on the seat, I found one at a bone yard for $25, different color tho.
Replace all under hood fuel lines, I'll bet that film goes away.
Transmission is a whole 'nother thread. You may be able to find info using the search function.

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83 SD

84 CD

Seat is not that big an issue or a deal bearker- as long as the seat is not torn/ripped.

Couple good write-ups of "restuffing" the seats with foam, pool noodles, etc.-I have done all my MB seats and had great sucess.

Oil and tranny...I leave to more skilled forum members

Oil leaks are _NOT_ normal. At all. And the repairs can either be dirt cheap (valve cover gasket) or fairly expensive (rear seal).

Since you don't have the experience to evaluate it yourself do not buy before getting someone experienced with these particular vehicles to look at it.

The cloudiness in the rear window is due to it delaminating. It might not be leaking water yet, but there is no fix for this short of replacement.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

A rear window can be picked up from PNP for about $45. a new one, very pricy. I think PNP in AZ has 50% sales quite often.
The rear corners getting milky is a common thing when the gasket get cooked in the sun after many yrs. water wicks in between the layers of glass

the W126 has a rear laminated glass with the defroster wires between the layers.

Keep checking for the new arrivals, you will find some nice ones coming in from time to time with almost perfect seats.

once you get the MB bug, you will have a yard, garage, barn full of parts .

there are several members in the Phoenix area I see on here from time to time.

the price seem a little high with the problems you describe.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works