I have had the same problem before.. It sounds like the seals are leaking and not applying adequate pressure to the clutch packs. I know it's a no no but I put about a cup and a half of brake fluid in mine and it made it work.. When it quits, hopefully it will be warm and I will rebuild or replace it.. I was not out to try it.. Some people say that it makes seals mushy.. It fixed mine.. for how long I am not sure..
Good Luck
Dan