One was the broken 2nd stage pump tube, well known issue and I'd wager fixed on any Independence that's out there. The other was an improperly finished hole in the pump linkage that caused excessive wear to a pin. According to AOA, a few did not get final finishing of the hole and were left rough.
In both cases, repairs were done quickly ( I fixed the pump, AOA sent me all the part free of charge).
I did have to replace the pop-off seal last year, it was the source of a slow leak and I replaced the original with a delrin part I made and have had no issues since.
I love mine. I don't own a compressor, tank or any other paraphenalia. It's not for every one but suits my shooting perfectly and BTW, if you do get one (or probably any ST barrel), I highly recommend taking a look at the H&N Sniper Magnum pellets. They outperform the JSBs in my gun by quite a bit.
Also, I added a baffle between the end of the barrel and the end of the shroud and like it very much.