If it is like the one in our 5th wheel (Alpenlite), it also may have a filter under the counter, that being the case, it could be full of crap/debris, and passing that debris into the valve body. Once the filter has been removed, (if equipped), you could make up a straight piece of hose/pipe so the assembly receives full water pressure from the pump/city water supply. Then it might have enough pressure to push any obstructions through the valve body, which might cure the seepage. It's worth a try, if equipped with a filter.
In checking my Coast Distributors and Northwest Trailer Parts catalogs (for my mobile RV Company business) I don’t see that device listed. My guess then it’s a part WRV purchased from Lowes or Home Depot, and installed into the system as a benefit to the owner. Not something other Motorhomes have, our apex does not have one.
So if the above treatment does not fix it, turn of the city water, (water pump), bleed down the water pressure, (to be safe turn off the hot water heater as well, in case you put too much air into the system, you don’t want to boil the tank if possible) and then remove the device and take it with you to the store. So your fresh water system is not off line and so you can use it. Plug the pipe with the appropriate sized fitting so you can then use the system until you find a replacement.
Hope this helps.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech