All of these M103 (and M104) engines will leak oil from the front of the engine at the cover for the timing chain at the 'c' shaped area where it meets the head.
It is very easy and cheap to reseal these.
Remember to insist on taking home all of his maintenance receipts for your file.
Also, you've heard this before, but in the words of Hans and Frans from Saturday Night Live (in an Arnold Schwarzenegger accent), "Listen to me now and believe me later", it is also a better idea to pay full price for a clean, well-maintained MB than to get a "deal" on a questionable car and try to bring it back to life.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".