Rt classic needs help

[Special_kid]

a friend of my just got a use rt classic and since i have 3 agd markers i thought i would try to fix it for him.knowing that there aren't that many parts i though this would be easy. after i first gasses up the marker i noticed that the trigger didn't charge and a large leak came out of the back and front of the marker.I took it apart checked all the o rings and replaced the 2 on the rear assembly screw. This did not fix the problem. Is there a part that might be missing that would cause this problem??? i checked the trigger rod lenght and it looks good 1.935 what agd told me to have it set at. I'm stumped and about to rip apart my rt classic and see if there are any parts it has that this one doesn't..
thanks

[Dayspring]

Check and make sure that the reg piston has an oring on it, and is even there.

Next, check and make sure that the powertube orings are in good shape.

Lastly, make sure he has an on/off pin.