Interesting as usual, thanks
I had a canister once. It was a screw thread type. When I unscrewed stove there was a slow leak. I just left stove on until it was empty. Must have been dirt between valve and valve seat like you mentioned. This was probably 1 of 30 canisters I've bought.
My Coleman Exponent F1 developed an annoying property. First, a couple times I didn't screw it on tight enough, it leaked around side, and caught fire. I just blew it out and screwed it tighter. Maybe the flames damaged a gasket or something. Then, I screwed the stove on tight, used it, and left it overnight when it got to maybe 32 F. When it got cold, the fuel started leaking out and it was empty in the morning. It happened with several canisters. Must be one of those tolerance issues you talked about.