The injection timing error does not necessarily indicate timing chain stretch. Unless you have full and complete records for this car, you don't know if the pump has ever been serviced or adjusted before.
The ONLY way you will know for sure about your timing chain stretch is to measure it. To do this problem, you need the exact MB procedure and a dial indicator. You can't really know for sure by merely lining up the marks.
If the engine has had religiously frequent and thorough oil changes, there should be no stretch. This is not a timing belt on a Honda, it's a steel chain. The original one in my 240D (same chain as a 300D) went 380,000 miles and was in good shape when I replaced it at the 380,000 mile overhaul.
PS Don't perpetuate the diesel shop's customer discourtesy by continuing to do business with them. You are a paying customer and should not have to put up with such discourtesy. LB