If you know this person, make sure you quiz them about the oil consumption. Study the records and see if the valve seals have been upgraded. When upgrading, the valve GUIDES were not upgraded, only the valve seals. To replace the valve seals is not a real big deal, this is done with the head in place. If they were upgraded early on AND the owner reports no oil usage AND you believe her, then this is probably no problem.
The achilles heel on these cars is DEFINITELY the climate control system. The controls fail, flapper valves fail, evaporators(the worst nightmare of the a/c system on this car) fail and compressors fail. If in the records you find that it has already had an evaporator this is a plus. The evaporators are bimetallic and if it has been upgraded to an all copper evaporatr, the worst climate control nightmare is taken care of.
The MB Buyers Guide states that in spite of the climate control system that these cars are "your best buy in a used MB period, end of story" or something like that. This is a strong statement that I read before buying my 300E that I have now put about 100,000 miles on, bought it at 80,000 miles. I now know how true that statement is.
Best of luck,
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in