The Gen 2 rear axle uses only 5 PSI to engage the locker. So if you sent 15 PSI to it, you probably blew out the diaphragm in the diff.

Most of us use the factory pump to avoid blowing the diaphagm since it has a built in regulator and a let-off valve to release the pressure.

Its seems like a common problem for these to leak, A few guys here bought diaphragms from the dealer and replaced them..I think they bought out the last of the stock. There's a later version that might still be available, but not sure if it will fit your diff.

99 Gen 2.5, fixing blown head gasket
89 SWB- 33's, ARB Front locker, SR rear locker/axle, SR F brakes, winch, WST Offroad Armor all Around, 2.85 Aussie T-case Gears (SOLD)
Sold: (2) 95 SR's, 86 SWB, 90LWB, 91 LWB
-Can Change a timing belt in my sleep..