LOL...two statements you don't often see in the same sentence....
Selling the Tau 7 should net you enough to replace it with a S/H IZH-46, which is quieter on discharge (the pellet will still make the same noise on arrival) and just as capable as the Tau.
Getting hold of replacement seals for the Izzy is an interesting exercise though... Tau ones are common as muck by comparison.
Although a friend seems to be having some luck with a workaround using standard o-rings - time will tell if it lasts.
As for storing CO2 guns gassed up -opinion varies, but I'm still of the opinion CO2 guns are best stored without gas in them.
A S/H FAS is another possibility...