Bummer on that sucker starting to leak again... I've gotten them auto parts in the past. I'd probably try Napa or Quest. They seem to carry the better stuff. Sometimes.
But, there's not much that can go wrong with these buggers. You just happened to get a leaky one. I have gotten a couple of them from salvage yards and always had good luck with them. Just look for one that's not leaking.
Since your prop valve is going to be replaced anyway, I'd be tempted to take that end off and see what's inside. I'm curious that way.
