Hi zumzum,

An "ordinary" fill valve like used on virtually all other RVs will work
fine.  You will install a bleed valve in the hole where the little tube
comes from the fitting on the tank that's about 8/10 of the way up the tank.
This is the overfill port and lets you know when there's 80% liquified
petroleum gas (LPG) in the tank by emitting liquid petroleum gas as opposed
to, well you know...

Local propane shops will do the deed for ~ 40USD.

David Beierl has knowledge of the location of a rebuild kit.  So David, if
you have that pointer please post for us.

Like the funeral director signs his letters,

eventually  yours,

pensioner