My 2017 YH Hardcover without autostop has been filling my three 30 minute SCBA's going on 8 years now without a rebuild. I use ice in the water which keeps the temp below 45C and use Mobil Rarus 827 oil. I have spare parts for when the day comes but (knock on wood) haven't needed them yet.
Here's the AT44 o-ring list that I found several years ago. The barrel o-rings are #608. Here's a link to them on O-rings and More: https://www.oringsandmore.com/metric-buna-o-rings-7-66-x-1-78mm-minimum-100-pcs/
My Avenger does not have a breech o-ring. There are two o-rings on the pellet probe that seal that area so no worries about damaging a breech o-ring. I use goo-gone to clean new barrels and non-chlorinated brake cleaner for subsequent cleanings. I have recently been using Johnson's paste wax...
I love shooting steel and have many AR500 targets and a KYL. Steel gives you instant visual and audible feedback and a quick spray of white paint instantly renews the target. Especially like that quadrant target. It was the most fun target to shoot at the 2019 GTA Fun Shoot.
The same thing happened to me when my valve stem broke at the 2018 GTA Fun Shoot. I had several pellets stuck in the barrel before I realized that the valve stem failed. I degassed and disassembled the gun and pushed the pellets out. I then sent the valve to Troy Hammer for repair. He made it...