I have a boat with a 1972 65 HP Evinrude. It worked great last year. This year when we put it on the lake it would not shift into reverse. But when you just hook it up to the hose in the yard it goes in just fine. We also had it out this last weekend and it some how slipped into forward from neutral all by its self a few times. Now when you try accelerating it seems like it keeps slipping out of drive and then quickly back in. Any ideas? Thanks!!