What is going on with my Merc trans?
 

Upon starting the engines after they have sat for 24 hours, the port trans will not go into reverse unless I put it into forward 1st then back to reverse. The transmission are Merc transmissions from 1978 and they are mechanical shift, NOT electric shift. Neither trans slips and the fluid smells good, and the prop on the port drive does not spin when the boat is on the trailer and the engine is running in neutral.