My mom''s 1990 300SL is having trouble going into reverse. It tends to happen when we first turn the car on and it's cold. I pur it into reverse and nothing happened. It seemed kinda stuck. Like it was in the gear but not moving. I checked the parking break and everything. The car had no trouble when we put it in drive though even though it wouldn't go in reverse. I'm not sure whats causing this just needed some help or advice. thanks

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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.