I notice that your RV is a 2013 model. Your grey water valve can not be "worn out", and for that reason it makes me think that it may have developed a fault.
The valve is held in by 4 small bolts (if it is anything like I have seen). I would suggest that you empty the grey tank - then take out the 4 small bolts and remove the valve. Then - because the valve is relatively inexpensive and ready available (many Walmarts will have them), I would suggest that you put a new one in. Beware: The valves comes in different sizes, so make sure you get the right size first time
If you can use a socket set, it's an easy fix. If you are not handy with tools, then clean out your grey tank extra carefully, and after this you can most likely talk you "friendly RV neighbour" into doing it for you. I would if I was staying next to you.