I bought my 92 300D in October 2001 with 130K. It now has 165K. Since purchase:

Replaced all belts and hoses
Replaced fan clutch, tensioner, and fan
Replaced two front struts
Preformed major service 2x (all fluids and filters)
Replaced thermastat
countless gallons of Rotella-T, and MB filters

On To-Do list:

all brakes and rotors
burnt out aux fan
4 new tires
refinish rims
radiator if needed
recharge a/c
and whatever she decides to throw my way

So far I have spent $0.15 per mile ($1,500.00) doing as much as I can myself.

I was not in position to do my own oil changes (in LA you have to recycle the oil -- not always easy). Be smart with mechanics. I often bring in filters, and even oil and pay for the straight labor. I do the same with any parts that need changing, such as brake pads -- it gives you a chance to shop around or send for by mail and keep the costs low. Be careful who you choose for a mechanic.

so far, I am seeing about $700.

Although it is very difficult to seperate the items of neglect from the everday wear items. And the initial money spent on immediate repairs when you first buy a used car borderline the category we call 'impulsive'.

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I'm in the hole for well over $1,600. For that kind of money, I have done:

1. Front end (both tie rods, lower ball joints, sway bar bushings, one UCA)
2. Brakes (four disks, 3 calipers - THESE buggers were expensive! 4 sets pads)
3. Alternator (this one took me by surprise and left me needing a tow)
4. Four bundts complete with winter tyres (painted, they look better than my summer tyres!!)
5. Pioneer iPod-ready receiver
6. Oil, filters little rubber things here and there etc

The big one was the front end. I removed the Tie-Rods myself with Bens lovers help, but we couldn't get the UCA out. After looking at where the upper sway bar bushings were, decided to drop it off at a shop that my mechanic recommended. Cost me $750 labour for that one!

I'll have to say though, the parts for Merc are really reasonable for the quality you get. Its the best car I've driven so far in terms of sheer comfort and reliablilty and with all the parts I've changed, I know I wont be worrying about my brakes and front end for sure!

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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

Preventative or necessary?

Necessary:
Alternator(Upgraded)$120
Rear Axles$200
Oil Pan Gasket$20
Filter Changes$150

Around $500 sounds right to me

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

My SD is the most trusted in the family,and my family treats it as such.
So like my children it is given the same love and respect as other members.
I'd say last year,maybe $400 in fluids,and maint. parts(belt,regulator,glow plugs).