[rheavn]

I helped a friend with that same manifold.  We replaced every push in fitting AND shut off valve we could see in that compartment and his 2015 started holding air.  We sourced the replacement compression fittings and shut off valves from McMaster Carr.  The Valid shut off valves are plastic-----replace them with metal ball valves.

Once you get your coach air tight, you will wonder why you didn't do it sooner and the enjoyment factor goes up accordingly.  If you just replace what leaks you will be chasing leaks forever----which is very frustrating!

Did I mention that I hate plastic..........................................