If it is leaking outside by the brake actuators, you have a diaphragm going bad in the actuator. This will not cause a loss of braking, but it will cause the rear emergency brake to apply unexpectedly or the safer action they will not release. This will not allow you to release the brakes and move the coach.
The pressure is perfectly normal and is controlled by the compressor mounted governor. No system made will use a pressure safety valve to control pressure. they are safety devices only.
If the leak is in the drivers control valve it will have to be replaced. I do not know if the newer valves can be rebuilt now days or not. Use to be able to just disassemble the valve and replace the rubber parts inside. Probably not cost effective now days to pay shop rates to rebuild a relatively cheap part. Good luck and be safe. Ed
GSMC(SW) U.S. Navy (RETIRED) 1967-10-03 to 1993-11-01
1995 Gulf Stream Scenic Cruiser, Cummins B5.9, Allison MD3060, Toad: 2005 Focus ZXW SES Wagon