You are not the only one who experienced this problem. It sounds like Mercedes modified the replacement sensors because, over time, the metal housing on the sensor was bonding with the bell housing. Here is a long string that involved the same problem as yours.
M119 Crankshaft Position Sensor R&R - Benzworld.org - Mercedes-Benz Discussion Forum
This guy eventually gave up and took the car to the dealer who was able to get it out by drilling and picking. Some in the above link suggested just knocking the sensor through and picking it out through the vent holes in the bottom of the bell housing. Another suggested that if you knocked the sensor into the bell housing you wouldn't have to pull the transmission completely -- only separate it enough to slide the sensor out between the bell housing and engine.
If you plan to drill it, one poster suggested that you remove the transmission mount bolts and lift the transmission up so that it will cause the engine to move down/forward and will give you more room to access the sensor.
I haven't changed mine but I will definitely be interested in how you finally deal with this problem. Best of luck.