I can't seem to keep the "O" rings sealing the valve spools at the top of the main hydraulic control valve cluster in my MF750 from leaking. New Buna N "O" rings don't even last a season. After you change the "O" rings a couple of times, you have to change all the JIC fittings to keep them dry, which isn't cheap.

Last season I tried Urethane "O" rings in a hard durometer 90, which seemed quite dry in use, under pressure, but now leak badly with the combine resting.

Is the problem combine chaff working its way between the spool and O ring? I know combine chaff is the main ingredient of all the rad plug powders and liquids on the market.

The valves on my backhoe, which see a lot more use, are quite dry after 30 years. I would have thought that earthy dirt would wear O rings faster.

The combine spools don't appear to have any sharp edges. I'm afraid to try emery on the corners lest I break through the chrome plating and cause a major corrosion problem.

Should I be trying to figure out how to install a wiping seal or bellows to keep the chaff from getting to the "O" ring?