My '77 300D made lots of noise (knocking/nailing) until it was warmed up also. I guess that's part of the charm of owning a diesel, the sound of pennies in your piggy-bank, as they say. I've heard that could be weak glow plugs, but I used Red Line Diesel Fuel catalyst in that car, and it claimed to reduce "nailing." It's pretty cheap ($4.59 at Pep Boys, I think). It didn't do any harm, and a couple times it seemed like the car had real power(!)
The local independent garage in Allentown PA recommended 150K miles as an interval for changing the timing chain, 100K for gas engines. Not sure what MB recommends.