You might actually be able to simpley take the motor apart and reconditioning it yourself I was actually able to do this. Heres the post. If uyou have any questions feel free to ask.
finally fixed passenger side window

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W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.