Our team got insights and were having a few problems like this, Lettucecheesecake was there! As he said try the noid, we were finding them gunked in lube, causing one oring to pop off, get pinched and making the gun just puff, if that's the case, then it'll be the second one from the bottom. Bad news, is they're special order and you have to get them straight from Bob. We got lucky and got some from http://www.pneusol.co.uk/ however they just pulled some orings off a noid they had lying about, I don't think they had a supply of them. I was finding the stock orings to be pretty awful, On all bar 2 of our guns, the rear two orings on the rammer were getting deformed, causing the gun to barely cycle. You've got to smother these orings in lube. If it's still playin up, and you have the 1.9x5.8 oring in the shut off then I would highly recommend replacing it with a urethane 010 D70, the 1.9 is just far too tight for our weather. We did and it made a huge difference, I've gone as far as putting an 010 xring in it's place and its even better now. Make sure the dwells at 12, atleast at this time of year anyway, anything under that and they seem to start acting funny. Now we've done all that, they're easily shooting 3*/4* grade paint in 5 degree weather.