Lots of folks can rebuild an engine from the ground up, but on these cars, the rebuilding of the engine is just the 1/4 of the way home. After the rebuild, you still have 3/4 ways to go to get it right. You can have a perfectly rebuilt one of these engines and it still won't run right. Sometimes, I think Mercedes engineers be complicating things just for the fun of it to make mechanics not want to work on their cars and run the other way when they see one coming toward the shop, especially diesel cars. If it was easy, everybody would be driving a Mercedes diesel.

Anyway, it looks like your problem might have been the turbo from the beginning with the sudden blue smoking issue and looking at your picture after the head gasket replacement. The head gasket is probably on right, if it weren't, the car wouldn't even run because of low compression from an incomplete seal of the head gasket that is if the mechanic even get the car to start at all after the head gasket replacement. So, since the car is running, that part is probably ok. Your timing is probably off now with all of the black smoke showing on the exhaust manifold. It is almost impossible for a first timer to get the timing right in less than a month and make any profit. Usually, it ends up costing the first timer to fix these cars no matter who it is or how much experience they have working on other engines.

Conclusion, your mechanic is a pretty good mechanic to get this job done in a month and have your car running any kind of way. Your timing will probably need to be reset. And your turbo will probably need to be replaced, which looks like was your problem from the beginning. Also, the tell tale sign of the timing being off is your hard starting in the mornings, unless you were burning that home made grease fuel. You would have had to pay me over $2,500.00 to do that job, if I would do it for you for that price, so I know you paid at least that much to a professional; so I wouldn't trust taking it to a another mechanic to mess it up even further for another $2,500.00 and the car run even worse. Therefore, I would let this mechanic keep practicing since he is pretty good to get the car running in a month on the first try. Take it back to him and hope his nerves aren't shot and he will take another stab at it to try to smooth it out. If you haven't spent $5,000.00 yet, then you are still looking good.

BenzDiesel