Corrosion is one thing that could hold these locks up. You could try this if you'd like. Get a spray bottle and some muriatic acid "pool acid " shoot the locking mechanisms and let it do its job about 4 minutes. Rinse with water.... With the drive all the way down, put gear in reverse and lift on drive to see if it works. The round plunger inside the housing is usually what gets hung up so you might need to move it back and forth until it frees up, if you can free that up, than you should be good to go. If not, you'll need to order some new parts.
#50 is usually the problem.
Unless the release rods#43at(#9) locked in the down position??
Sometimes the rod where it comes through the arm right at the #9
it gets pinched there and will keep the lock locked out.
