Michelemarie,
Welcome to JOF
If your RV is still under warranty your dealer can install a new valve. But, if your RV is out of warranty there are a couple different ways to replace the leaking plastic valve.
Anytime a plastic valve becomes an issue in my TT's I replace them with a metal valve when possible......., and in most cases utilizing SharkBite push-to-connect fittings compatible with the 1/2" PEX plastic hose. SharkBite connection fittings eliminate the need for special PEX crimping tools. Lowes, Home Depot, or a local hardware are a good source for PEX plumbing fixes.
Bob
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2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)