Depends on where it is leaking from.
Most common leak points are:
Tubing not sitting well on barbed fittings. Often fixed with a dab of superglue to help keep it on straight - use sparingly and removal isn't normally a problem.
Bolt sail o-ring isn't sealing.
Bolt stop o-ring/s not sealing (less common than first two).
And the o-ring inside the breech right behind the feedneck is either not there or not sealing (easy to miss and sometimes completely gone).
Try swapping bolts from the working to the non-working. That will eliminate the bolt o-rings.
Take the grip panels off and listen for leaks - if you hear it from inside the frame it is often tubing or perhaps a missing o-ring/gasket on one of the fittings.