You are 100% correct. Although, up here in the frozen north where people generally only use their A/C about 3 months out of the year, or less, the O-rings just dry up from no oil on them. Charge the system up again, and sniff for leaks with one of those little electronic sniffer gizmos, and no leaks are found. The shop I work at doesn't do A/C (due to the aforementioned licensing) but we send them out another local shop that services them. They add UV dye to the system too, and there have been many that just leaked out because they weren't being used and the O-rings shrunk up just enough to cause a slow leak.
When I was in Arizona, we saw about a tenth the amount of A/C problems as here. Mostly because they were being used a lot more, and the systems stayed nice and lubricated.
