1992 Mercedes Benz 300te Removal and repair of ignition key

Earlier today I inserted the ignition key into the ignition lock on the dash, however the key would not turn in the lock and the key is difficult to remove from the lock. I have tried both keys that I have for the car with the same results. One key is rather worn, but the other is still like new. It appears that the lock cylinder is damaged, or worn out. I have removed the dash trim to expose the lock mechanism but do not see how to remove the assembly from the steering column, or the lock cylinder from the assembly, especially since I can't turn the cylinder with the key. Since I cannot turn the key, I cannot get the car out of Park to even move it out of the garage. My questions are:
1)What is the procedure to remove the lock cylinder? 2)Can the cylinder be removed without removing the whole assembly from the steering column? 3)With the cylinder removed, can a locksmith repair it or does it have to be serviced by Mercedes like the milled keys?