Larry is right, and if you're mechanic hasn't sealed a timing chain cover before, then he must not be a Mercedes mechanic or is hopelessly "green".
Leaks from the timing chain cover are very common on M103 and M104 engines. I'd find a new mechanic.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".