Just an update to this problem. Local mechanic finally got around to helping me with the tratcor. Pulling off the PTO valve was embarrasingly simple. Undo linkage, couple of bolts, some light raps with a punch to break it free, and it pulled off. It turns out that the actuator rod that enters the valve actually runs all the way through the valve and protrudes out the other side, fixed by a c-clip. The mechanic pointed out that you could look behind the c-clip and see that its not a very good design. Its open into the valve, with only an o-ring behind it. We freed up the valve after soaking it for a time. A big gob of grease on the end should keep moisture out now. Valve now works like butta!