I recently acquired a 1982 782. I was mowing with it, and noticed a tendency for it to want to keep speeding up, so i figured i better check the transmission fluid, and sure enough it was low. I bought some more; figured while i was at it I might as well drain it all out, which i did. Fire it back up, and there is a steady stream of oil coming out of the top of the transmission. It is leaking out of the 1" nut that's on top. I need help, why is it leaking out of that nut, and what can I do to fix it?