If your HPR is leaking then an oring or seal inside is faulty. It really just depends where the leak is coming from. That could also be the cause of low velocity if your HPR is creeping the valve pressure may be too high for the LPR to open it up, or if air is leaking out around the HPR core then you won't have enough pressure build up to fire the ball fast enough. I would swap the outer core orings first and see what happens. Make sure the oring on the groove at the top of the HPR body is in good shape as well.
As for the screw, once you get it out you should be able to re-tap the hole for a new screw of similar threads....depending on the damage.
CCI stock class Phantom pump f/s. This thing is LNIB. Comes with stock magazine, extended magazine, barrel detent kit, crossfire lite up dot sight, velocity adjustment tool, 12 tubes even the barrel blocker
Ninja grey 50/4500 paintball tank f/s. Hydro good until 2019
Old school angel poppets/cup seals(LCD and A4/speed), spring detents(not sure which models) F/S