Eddie,
I have a 94 E320 with the vacuum locking system, and I assume your SE does also. I could insert the key into the dirver's door lock but could not turn it. The passenger's door lock and the trunk lock worked fine. A new lock from Meercedes was needed. Take proof of ownership to the dealer, he will order a new lock, and your current key will work in the new lock. It cost me about $280, and arrived in one day. Takes about 10 minutes to install.
regards,
Mark