I was essentially GIVEN an 84 300SD (cost of back registration, tickets). It has a lot of miles on it -- 370K. The guy that gave it to me got the car in a real estate deal (the car was garaged in the house that he brokered, and he had to get it off the property) He doesn't have any information or maintenance history. It seems to run fine. there is some vibration at idle, it is a bit slow in 1st gear, even though it is turbo. I am able to take it up to safe freeway speeds in Los Angeles County. the interior is in really good shape, only a few small tears in the headliner.

What should I expect for 300SD at such high mileage? Anything I should pay particular attention to? Are there any expensive, unnecessary things that I should steer clear of when I take it to a local indy German Auto Mechanic? I am a veteran of '68 - '74 VW Bugs, and was my own mechanic, but now absolutely nothing about diesel engines. I am pretty impressed with the shape that the car's body and interior are in, which is why I am going to put the effort into it. It's a beautiful car.

 

If you plan to keep the Car and do as much work on it as you can; I would buy the Factory Service Manual CD set directly from the Mercedes Classic Center. It covers the whole Car extensivly except for rebuilding the transmission. $19.99 +$7 shipping. It easily pays for itself (there is also an owners manual in there also).
http://www.classictechlit.mbusa.com/...ssicTechLit%29

I am going to send a private message that will have a bunch of do it yourself links so you can get some idea what is needed.
You will need to know how to bleed the Fuel System incase you run out of fuel or change your fuel filters.
How to do the Valve Adjustment (no Hydraulic Lfters).
A loss of power often indicates plugged filters (2 under the hood and a filter screen in the fuel tank).
Common areas that can leak air into the fuel system Old Style Hand Primer and Old Fuel Inlet Hoses.
And eventually you will need to check the Timing Chain Stretch (I am not making this up) and the Fuel Injection Pump Timing.
Also if you have the origional Vacuum Pump on the Car you might want to pull that off and inspect the parts that drive it. When the parts go bad back there they dump down into the Timing Chain Drive and often break the Chain causing Pistons and Valve to collide. You would be looking for too much play in the Ball Bearing and the Pivot Arm.
Take a close look at the Oil Cooler Hoses for leaks; one of the major causes of destructive loss of Oil Pressure on High Mileage Cars that have never had the hoses changed. If they leak badly while you are driveing on the Freeway you may not know it until your Engine is suffering.
If you decide to replace them; removing the Hose Line Nuts from the Aluminum Oil Cooler sometime results in stripping the thread off of the Oil Cooler Nipple.

There is a do it yourself repair for this and Mercedes has Steel Repair Nipples to fix it ivolves cutting off the old Nipple and drilling and tapping for the new Steel Nipple.

 

I forgot something.
Despite haveing been a Diesel Mechanic for 18 years I found that when I removed the Front Wheel Hubs (to remove the Brake Rotors) and set the Wheel Bearing Clearance by hand as I have done with all the other vehicles I previously owned did not work.
I ended up getting it too tight and heated the Grease up enought that I had start over including cleaning out the over heated Grease from the Wheel Hub.
Next I set is like the Service Manual Said with a Dial Indicator (Harbor Freight sells an inexpensive magnetic base and Dial Indicator set that is adequate; lot of their stores in CA). No problems for 2 years now.
Part of the reason for the above problem is that the Wheel Hub Retaining nut is differant form "normal" cars. Hard to get a feel with it.