If your 94 E420 is like my 88 300e (which I'll assume it is) the actuator is very easy to replace. Now that you have the door panel off most of the work is done. To find the actuator, follow the yellow vacuum tubing in the door to the actuator. Shouldn't be very hard.
Anyway, I believe that it is held on by 2 or 3 screws but most importantly the actual lock is screwed in the tob of it. Unscrew these screws and the lock and it should come out.