My external service valve has a small leak which isn't a major problem, but it's a pain when you get a handfull of oil everytime you use it! Especially if the rubber gaitor is full when you close the valve!!!
I can't seem to find any information about how the valve is retained, if it is replacable, or if there are replacable 'o' rings.
They were held in place by a spring loaded detent ball and a small threaded plug or cap...threads in from the underside of the casting if I remember correctly. It is accessible without taking the whole casting off the tractor.
There was a seal behind the gaiter, presses into the casting.
Don't know about availability of spares. Seals, springs, ball bearings, plugs and the like are pretty standard hardware items.
Measure what's there and you should be able to come up with something....
The spool valve itself would be more a specialty item....
Ford listed four sizes......
The parts book, available on this site, shows a decent exploded diagram.
