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.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".