It's the o-ring on the RAPS pin. You have to remove the tank fron the RAPS, then unscrew the pin holding the lever in place, there should be a spring behind the lever, then the pin should come out the front. Swap out the o-ring, lube it up, and you should be good to go.
On a side note, make sure that your tank o-ring is good too.
Graphite Dangerous Power REV-I
– TechT bolt engine, REV-I & Disruptive barrel kits, Prophecy V2 w/ Empire feedgate, Crossfire SS 68/4500
Maroon and Polished Aluminum Dangerous Power Threshold
– 7th Element board, TechT bolt engine, magnet trigger kit, REV-I PMD, Sly Dual Carbon barrel kit, Prophecy V2, Crossfire SS 68/4500
Black and Silver Dangerous Power F8
– APE Rampage board, VS bolt, magnet trigger kit, F8 gauge, REDZ barrel kit, Halo B w/ Exalt feedgate, PMI 68/4500
Polished Aluminum and Red Dangerous Power F8
– Virtue board, VS bolt, magnet trigger kit, Halo B w/ Exalt feedgate, PMI 68/4500