I changed the whole thing not just the seals

Yes I've even cleaned everything and then wedged the pedal and left it for a while to Check for leaks but still nothing

Quick question. I've got a defender 90 300tdi. I had to change the front calipers as they were shagged. I put new ones on and also changed the master. I've bled them and seems to be no air in the system. Drove it for a month or so absolutely fine. A day later the problem started happening...