I recently had a slow puncture repair sorted which turned out to be the valve itself leaking. I was surprised that all the local based nationally known tyre specialists did not have a replacement steel valve. They were very keen to use a high pressure rubber valve that they said they fit to commercial vehicles but i wanted steel to replace like for like. I had to travel to a HGV tyre specialist to get one who confirmed that motorhomes should have the steel valves. My tyre pressures are 50 front and 75 rear.
I have since bought a spare from eBay in case another goes.