I’m looking at a 90 for sale.
owner says no reverse, rest of trans ok. Still using car.
Ideas on the issue like solenoid?
im assuming no way to fix without dropping the engine?!

 

Could be a valve body problem - A scan with a compatible tool would be a good first start -

Transmission comes out by itself from the bottom - Support the engine from the top, move subframe out of the way or remove, trans comes out the bottom.