The dip tube o-rings that came on the kegs I've bought from soda distributors have a square cross-section instead of round.
Same for the plastic ball-lock disconnects.
I've never had a leak due to o-rings. But I have had poppets leak on kegs that are waiting their turn in my non-kegerator refrigerator - with nothing connected to them.
I drilled an 5/8" hole in the bottom of a film canister (remember when cameras used film?). Place over the keg post so it sits on top of the o-ring, and add a little water - a leaky poppet will be readily apparent.
I just read through all the threads here and I didn't see any mention to replacement o-rings for the pressure relief valve. I've google'd and I see a lot of PRV's advertised as having replaceable o-rings but nobody seems to sell them or even list a size. Does anyone have a size or source for that o-ring? I've attached a picture of the type of PRV that I have, I don't know if there are any different ones.
They are universal valves with replaceable o-rings.
Been using these a month now.... retrofitted 5 kegs. The poppets seem to fit well. Springs included are quite stiff amd long. They fit but you actually have to press on your posts during installation. The new poppets/springs limit flow significantly compared to the older style..... for example if I hooked up a keg with only some star san in it just looking for am O2 purge, with the old poppets my gas regulator would scream and the keg was filled in a few seconds, utilizing the universal poppets the flow is much more regulated..... same situation now takes 30 seconds and no feedback from regulator. It's also much harder now to press on ball lock fittings to top of the keg.... like crazy hard. Might switch to a metal type fitting instead of plastic.