Victim: 1995 E320 (W124) with M104 engine.
Problem: external oil leak
Questions:
- I just changed from Dino to Synthetic. Should I expect leak to diminish or get worse?
- If I do the head gasket job, I know to send the top off to a machine shop. But what about the bottom that stays in the car - how do you get that surface smooth and clean?
Is the answer to do it manually by hand with scrapers and sand paper? Stuff towels in all the opennings to prevent debris from getting in the engine?

In case you can't tell, this will be my first head gasket replacement.