Christopher, that is excellent information. Thank you so much for the clear explanation!
My bus looses pressure to 60 psi quite quickly, will stay at 60 for a few days but eventually loose all pressure.
There are no longer any arms or stop signs on the bus. These were previously removed and appear to be capped well as I didn't hear any hissing from those areas.
The set up of the TC2000 FE is a rear leaf spring system, with no rear airbags, and only front airbags.
Indeed when the bus is level and no-one is walking around inside I can hear both airbag valves leaking, and can see bubbles when spraying the tube that comes from the bottom of the valve. ( Curiously when I turn the steering wheel the hissing stops in one of the valves.
Beyond that I can hear hissing, and see the bubbles from this schrader valve that is hanging out in the tank dump box outside the driver side of the bus.
Spraying didn't turn up any other leaks.
Thanks again. Where could I track down a part number for those valves?
Would any leveling valve work? Like for example this one off ebay?