I still think either simply spark plugs or maybe valve stem seals on the poor starting problem. The valve stem seals aren't that big of a deal to do, probably not a good first time project for you to do yourself though.
Since the motor may have been apart recently, they may have goofed up and left out a part. It's possible. There's a little spacer that goes on top of the valve stem, they may have lost one.
It could be the cam, it would be pretty rare though for a 103 motor (which is what type of motor you have). i'm guessing what was wrong with it previously was a blown head gasket, this is fairly common. I'd get the straight story on what was done, this will aid in diagnosis. The noise that the engine makes, is it a constant "tick tick tick tick" that get faster with engine rpm?
The transmission leak that seems most common on this car is the front pump seal, it would be leaking from between the engine and transmission through a weep hole in the bell housing. It gets expensive to replace since the transmission has to be removed to fix it.
i'd start with the basics first, see if the spark plugs are worn out to fix the starting problem, also try to find out when the fuel and air filters were replaced, also when the oil change was last done, just the basics first. Are you sure the garage you took it to is familiar with Mercedes?