Not sure about accessibility on your 5er, but mine are just inside the driver side basement door, very visible and would be easy to change. Suggest you try to look straight up from the hoses inside whatever space is directly above, and follow the lines to the valves. If that doesn't work, how about emailing Jayco and see if they have a schematic of the water system that they can email you. Once you find the valves, I wouldn't think it would be difficult to change them.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.