w123 240d, oily carpet /driver side front
 

The carpet and floor mat are oily...looks and smells like dirty motor oil. It's only where my feet go, but the mat is slippery...did the PO work at Jiffy Lube and just put oily boots in the car, or is there a leak? The floor is dry underneath and the firewall looks OK too.

You basically have two options. On the back of the instrument cluster is an oil line that goes to the oil pressure guage. it can be loose or the guage can be bad.
Or, if the shutoff valve in the IP develops a torn diaphram, it will send oil through the brown vac line to the keyswitch. Look up under dash at bottom of keyswitch assy and see if it has oil drips. If that is the case, don't drive it until you get a new shutoff valve, as your vac system will load up with oil. worse case is oil fowling the brake booster. $$$
I've had oily pants legs from both of the above....:D

Is this 240 standard or automatic?

it's a 4 speed...

The autos are 4 speed also, but I'll assume you mean a standard. Excellent. A nice little addition you've added there.
You might as well take the homely little bugger on home. the wife probably won't appreciate it regardless......;)

the pressure gauge gives good readings, so I THINK it's not the problem, but I'll check that connection and go from there.

A small leak won't affect the pressure reading enough to change it, as it would go way past the peg if it weren't there. The oil trail will be easy enough to follow, regardless of location. Instrument cluster can be pushed out from behind, by reaching up from underneath. sometimes you have to push some slack in the speedo cable to get the cluster out.
Many posts with pics if you want a visual.

oil leak
 

If your car uses the master cylinder (inside near firewall, directly connected to the clutch linkage and a slave cylinder at the bellhousing), check and see if the clutch master cylinder is leaking. There is a reservoir on the firewall you will see dropping if the master cylinder is leaking. If the 240D is like the 220D in this regard then check master cylinder and reservoir level. If the reservoir drops and master cyl leaks then you are in danger of your clutch going out on you completely, likely at an inopportune time. Or, maybe it's the line for oil pressure or both. You can smell the difference between hydraulic and engine oil quite easily.

Excellent info Ralph. You can tell all I've had are automatics....:D :D :( :(

I left the oil pressure sender disconnected accidently when I was diagnosing some electrical troubles and it dumped about a quart of oil in the floor board in almost a minute:eek: . I've got most of it sopped up but I'm taking suggestions on how to really get it clean.

it's clearly motor oil, by feel and aroma. The pad under the carpet is gooey too, and I can't imagine how I'll get that clean. This is the most mechanically simple/primitive car I own, and due to neglect on the part of the PO I have a laundry-list of to-do's on this car.

You'll have alot of fun with that car, and mechanically primitive might just be an understatement!
I can't wait to one day own a 240 manual, be it MB OR Volvo.....

Fuel and/or Oil leaks, cleaning up the mess.
 

Fuel and/or Oil leaks, cleaning up the mess.
http://www.peachparts.com/shopforum/diesel-discussion/141355-fuel-oil-leaks-cleaning-up-mess.html

Keep us updated on what you find!

Motor oil is a nasty one...but brake fluid is pretty bad too!!!

The short version is, I blew it up. A con rod came through the pan and made quite a mess on the parking lot. It already had a noise that I was trying to ID, and I guess this means it was a rod bearing noise?!

Did you happen to check the oil before the blew the rod?

Maybe you lost enough through your leak to have low oil pressure.

Sorry that your engine is toast :(