Last year I bought my father's 87 300E (He was the original owner) with 50k miles on it's clock. I took it and the records to a super tech, and what was needed was as follows:
Change thermostat cover from plastic to metal
flush coolant - hadn't been done, ever!
replace water pump, leaking from coolant neglect - pressure test system
Replace heater hose, radiator hose, bypass hose, and heater pipe and elbow fitting
replace bad plug boot
flush brake lines
replace injector seals
replace mono belt
replace 10 year old tires
replace rusted out center muffler/pipe.
Do 60k service as part of above.
Top off the freon, add dye, identify extremely small leak - fix when the rest of the AC needs work.
Check that 3 factory service bulletins had been done on: 1. replacing the throttle bushing on the accelerator control cable with a more heat resistant material. 2. front flex disk upgrade/replacement at 30k intervals. 3. check proper connection of plug between air bag and wheel. Air bag replacement upgraded by 5 years fom replacement date on glove box sticker.
Has not needed anything non-routine since, but I redid the suspension with Sportline and the headlights with Euros.
Hope this helps.
87 300E, 65k miles
[This message has been edited by JCE (edited 11-16-2000).]