I would invest in a 129 DVD from mercedes, The seat covers from MB are way out of line if you can find them , look toward a company called GAAH, the install is tough but doable. The interior shop recommended by MB uses them they are as good if not better than OEM.
The locking issue is a little dificult to diagnose, (2) microswitches in the door locks start the pump under the seat, running forward pressure to unlock, vaccum to unlock, the remote does the same thing sensing the infra red and routing to the pump, but it toggles. You can probably find wood refinishers in Hemmings, or contact the MBCA (mercedes club) they will send you a copy of their magazine, I suggest you join.
The 129 and 140 cars had 134a and had threads plus a shoulder.