Yawns thanks for posting. My buddy Jim has a 1970's Avon that's why we're searching. Boat is still in great shape but slow leaks somewhere and we think it's the valves. Also, that valve design is slightly different in that it has that o-ring seal that you're talking about, so without that it's a little harder to pump than it should be.
I'll look too but if you find that valve repair kit would you please let me know and I'll do the same?