Belt stops spinning up hill, I just adjusted the clutch, its also very diffcult to catch reverse.:(:wall: Any ideas please?

20HP V twin Any common or known issues for these seizing up? Have on in the shop and it simply does not want to turn over. I was able to get it to turn far enough to verify both pistons are moving up and down. Also pulled the flywheel and all is intact and the engine still does not want to turn with flywheel removed. The crank under the flywheel had about 1/2" of pretty well built up rust and the upper bearing (what is exposed any way) looked fairly well molded up as in much moisture...(Pac NW is common for this white stuff on equipment left out) I have serviced this GT for several years now and it has always been only the usual, belts and mandrels and such. Never has used a drop of oil. Comments when it quit was that it was running, got off to put the dogs up and it just quit...quietly :o