my drivers seat on my 91' 500sl will not fold forward when the handle is pulled. I'm thinking that there is some sort of cable in the seat that releases it. My buzzer also sounds for approx. 20 seconds when the car is started. I'm thinking that the system thinks that the seatback is not locked

Sounds like the release cable is out of adjustment. Run the seat forward & tilt it so that you can release it. The seat will have to come apart to adjust cable.