I hear some people cleaning them with wd-40.. Might try that.. I hear that the 250's have that problem. If you end up going with different valves check out the Asco's cheap price and killer performance
I wouldn't use WD-40, it has a tendency to dry items out after it evaporates. Try some tool oil, it will stay lubricated and will still help you clean all of the parts up.
Any valve will leak if it gets debris in it. Take the valve apart and clean the diaphram and spring out with some soapy water.DO NOT use wd40!!! Use non chlorinated brake parts cleanerto clean the body of the valve.