PCP Newbie just purchased a Hatsan AT44S-10 QE

I got in some shooting with my new gun today. The first time I've ever shot a PCP. What a pleasure to be able to shoot an air gun without using the artillery hold. I put on the same scope I had on my RWS Mod 52 that I thought may have been ruined by that gun. Got the gun zeroed in at 25 yds, then I moved out to 40 yds and tried the 5 different type pellets I had. I eliminated 2 and moved out to 50 yds. Conditions could have been better, since I had some wind in my face. My final three pellets with 5 shot groups were Beeman Kodiak 21.2 gr with a 1 3/4" c-c, Crosman Premier HP 14.3 gr with a 1" c-c, and last was H & N Baracuda Match 21.14 gr also with a 1" c-c group. That's better than I have ever done with the RWS 52. I'm happy to say the least. Things can only get better once I get my crony , more pellets and some tuning. I think my scope is good as is. I'm going to need to purchase a 2 piece ring mount. The mount I have is a 1 piece, and I can't get the scope forward enough for proper eye relief.

Lamar

My first questionable issue with my gun came up today. I went out this afternoon on my back porch to pump up my gun, and I noticed an oily, cut open O ring laying on the deck where I have been pumping up my gun. It had me very confused at first, trying to figure out where it came from. I couldn't see anything on the pump that could have came apart, and then I remembered that one of the first things that I did yesterday before I ever pumped up the gun and started shooting was unscrew the air cylinder from the gun to examine it.
I unscrewed the cylinder from the gun again, and examined the fitted end, and it looks like there may be an O ring missing from a groove. Could I get confirmation on this from someone. Also, is it just a matter of finding the correct size at a local hardware store?
My guess is that this is a secondary seal to prevent air leaking. My gun seemed to maintain a charge.