Are you saying there was oil around the outside of the plug where it screws into the head? If so, that is leaking from the valve cover gasket. Not a serious problem, has no reflection on the health of the engine. If you go in to replace it, set the lifters while you're in there.
The shifter boots AND the 3 point upper link boot (under the seat) are very important. I would replace them, too cheap and too easy. Without them any rain water goes straight into the transmission. These tractors are prone to collecting water in the transmission even when the boots are good. Might want to check it, change it if it's milky.
The shifter ball should unscrew, try wrapping in a rag and using a pipe wrench. They are available on this site if it breaks.