What are you stuffing them with and how long do you leave them on for? I got leaks with mine but then stuffed it with a petite d'ssous bamboo insert topped off with an EP hemp booster and its been fine since then - last about 3 hours.
hmmm if it was just the older ones I'd wonder whether they needed stripping or does the pul need resealing (not sure that is the right term) but there is advice on here about putting them in the dryer for a couple of minutes for the heat to work its magic on the plastic. Someone will probably correct me on this one as I don't think I've got the terminology right!
I'd agree with Emma it could be the stuffing or have you tried a side snap? If its coming out from the legs have you got gape? The good thing about the side snap is you can adjust the poopers so have it tighter around the legs if needed.
I would try strip washing them and giving them a 10 min tumble dry on the hot setting to reseal them. What are you stuffing them with/? I would keep them and try them again in a few weeks, Gracie went through a phase when her itti's were appalling on her, left it a while and now they are fine x