Mechanics who only have a scant knowledge of Mercedes or the CIS injection system tend to approach problems with the slash and burn technique - i.e. strat replacing parts until we find a solution.
It's better off taking time out and finding an Indie shop who have great experience with M.B.'s

Having said that most. Indies around my area send CIS and later similar injection systems cars off to a Bosch Fuel injection specialist rather than try and mess around with them themselves.

You are better off getting some pointers from on a forum like this than taking your car to a mechanic who will just throw expensive spare parts at a problem.