Tank 1: You should use a silicone based lube on the fill nipple o-ring. It may be as simple as needing to be lubed. If that is the case, as you can find more than enough of the warnings out there, don't use a petroleum based lube, use a silicone based one.
Tank 2: You may have to speak directly with Ninja about the pin. I am sure that they will take care of you perfectly. Does seem as if the pin is too long, and you are probably using standard ASA, not an on/off or purging on/off ASA.
As to the second problem, check your ASA for crap on the threads. Like burrs or the like. If the top ring is getting chewed up, and the second one isn't, then the burrs, dirt, or whatever are closer to the pin in the ASA than part that you first put your tank into. Or, as I said previously, you are using a standard ASA, not an on/off or purging on/off ASA, and as a result of the air pressure, it is grinding and chewing up your o-ring as you are unscrewing the tank.