In those pics it looks like the right rear outdrive cup is worn pretty badly. I can also see damage to the right rear arm where the inner hinge pin goes through. If the damage is as bad as it looks in the pic this could easily be causing the problem if it's letting the arm move back and forth. The worn edges on the outdrive cup can't be helping either.

I would fix those 2 issues and try again. I have never seen/heard of this being a problem. Hope this helps man!