I've tried two different brands of AC accumulators for my '88 Fiero in the past few years with no success.
The first one (Four Seasons brand) had bad welds on the fittings, and refrigerant leaked from the welds right after charging the system. The second one (Omega brand, I think) leaked past the schrader valves over the course of a few months. I replaced the schrader valves with higher-quality ones (instead of the valves that came with the accumulator) and it leaked again... so it must be the seats and not the valves themselves.
Who sells high quality accumulators? I see that Fiero Store sells one that's priced at double the cost of other replacements, but no guarantee that it's any different...