My front RC Valve isn't recessing at fully open it sits 0.5mm high, it closes no probs, the rear one is perfect opening and closing.

I slacked off the cables and moved the pulley by hand no problems, very easy with zero force to open and close, but the RC Valve wont seat deep enough into the recess. Im guessing its a build up of carbon behind the RC Valve or on the rear of it, just want to confirm this theory or try anything else before i remove them?