The purists may cringe, but I've had luck freeing up sticky tumblers with WD-40 and gentle key wiggling. Also, the original Mercedes key that came with the car is the valet key. It should work in the doors and ignition but not the trunk or the glove box. The two copy keys were from the master key and should turn everything.

__________________
-Louis
The Hills of Western Mass.
1985 300TD 327,777 sold to JB3
1985 300D 218,xxx
1987 190D 5 speed 338,xxx