I've changed the valve twice on my toilet now in 2 years for the same problem (same toilet as the OP's), as well as the flapper seal this summer. I have never changed a valve on any other toilet in any of the RV's I have ever owned.
I have read this model toilet is a bit of a problem child; next time the entire unit will be getting replaced.
2013 Ram 3500 Megacab DRW Laramie 4x4, 6.7L Cummins, G56, 3.73, Maximum Steel, black lthr, B&W RVK3670 hitch, Retrax, Linex, and a bunch of options incl. cargo camera
2008 Corsair Excella Platinum 34.5 CKTS fifth wheel with winter package & disc brakes