most of the time, the stuff you're getting from AutoZone is a refurbished unit. That usually means SAE sized seals in a Metric sized cylinder. They can get really really really close, but not always close enough. So if they have a bad batch, then you might be the only one helping to filter through them all.
If you think the part is wrong, then step up to the Z32 master.
I doubt that is the issue, but hey, if you're swapping them out all of the time, might be worth your trouble.