2000 model w202 c280
All my reference info says this was produced through model year 1999, but that database does have occasional issues with year cut-off.
The 1999 uses a 2 track key, and is typical for needing replacement of lock at the major service at or about 100K or so miles.
That said, you MAY have a issue that is not mechanical failure, but external influences:
For Situations where the key will enter and remove, just will not turn:
1. if you roll into curb, then turn off car... this bad habit causes undue pressure into the steering system, and to the locking bolt.
A. Put foot on brake, hold it there while....
B. TURNING STEERING WHEEL INTO the pressure, HARD...then, without letting go of wheel
C. Try turning key.
2. Try a key that does not have excessive wear, if yours is ground up. A copy may not do.. must be cut by code, either by ordering from dealer, or by locksmith decoding old key, then cutting fresh on a CNC machine.
3. If this makes no sense, because it seems I did not read your question carefully, I posted the above because it is a related issue, and it may have haooened prior to getting stuck IN the lock.
So, if the key will not REMOVE from lock, but starts, shuts off, etc....
4. Be sure you got no doodads, leighs, ornaments or other crap between shifter and dash.... obstructions will intefere with the shift interlock. There MAY be a shift interlock OVERIDE ( button to press, or place to poke in a #2 Tyconderoga pencil, to allow shifting and thus, removal of key.
A. Call dealer to find out
B. Post question on Craigslist Rant N Rave
C. Crack open the Mercedes Manuals that came with car... they should have any such overide explained..... beware of manuals that are vague, My Sprinter manuals are vague, scattered and self-contradictory
D. Try a few things:
4D1 GENTLY goose the shift lever toward park with 5 ft lb of torque... no torque measuring tools needed, just a little pressure by hand, and while applying this pressure, see if key will turn a little more to full CCW removal position
4D2. Check for shift interlock release, already mentioned above.... it will overcome a failed interlock system.
4D3. Remove ignition lock, and see if key will turn all the way off and remove in your hand. If you can not make the problem happen 8in-hand, it is in the lock bolt housing, another column component, shift interlock.
PLEASE do followup with the end result.
If NONE of the above work, you will likely want to replace the lock cylinder and locking bolt housing. But let the diagnosis be done by mechanic.... we are just the peanut gallery!