Leak problem

[Slipps {MWB}]

Hey guys, I sold a mag to a guy and it worked when it left there, and now it leaks out the barrel. The stats are:
ULE body
RT Pro valve
Lvl 10 bolt
the big rail (cant remember what it comes off of, but its really common)
Intelliframe
Bike grip


IDK what it could be. His tank is high pressure, 800-900 psi. But its still leaking out the barrel. He dropped some oil in the asa and took 500 balls through it and nothing. Im stumped, so I'm going to ask my teammates tomorrow but if anyone on here has any advice I'd gladly take it.

[OneSelfLost]

One carrier smaller on the Lvl 10 should do it. If not, swap the carrier O-ring itself out.

A leak down the barrel when the trigger is pulled and held.. It's your on / off. If it leaks when the trigger is not pulled, its the powertube (Lvl 10).