Sounds like you might need a new seat motor. Now that you know how they are accessed you could procure one at your local salvage yard.
In the mean time you could use a portable drill motor to power the seat to the position you want. The drive shaft should slip out of the motor and gear. It has nice square drive ends. Chuck one end into your drill motor and hit the button. If the seat moves thew wrong direction just reverse the drill.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.