I'm having the same problem. I have a couple of messed up valves and have been evaluating some replacement ball valves. They look to me to be better than the original ones with no wound cord seals. Nice metal ball valves with metal to metal seals. Remind me to bring them to the airport for the fly-in and we can all look at them. They are commonly available and look to me to be pretty much what Taylor would have used back in the 40s. The original valves aren't exactly "aircraft" quality.
Hank
hjarrett2
at cox dot net