Bleed nipples leaking

[Niall]

Getting really f*cked off now! Fitted my hispecs the other day, went for a drive and one of them leaked. Retightened the nipple and drove it again. Not as bad this time. Today i noticed it had been weeping again after the last drive so i took the new nipple out and replaced it with one of the old ones. Went for a normal drive and perfect. No leaks. Got into my road and thought id see what happens if i slammed the brakes on. Pedal went slightly soft and has again leaked. Any ideas? im fearing the worst that the seat inside the calliper is damaged