I bought an old H80C Hyster forklift at auction. I loaded and unloaded it and the clutch worked fine. I didn't use it for several months and now the clutch won't dis-engage. It's a wet clutch and looking in the top cover it is clean. I believe the clutch has a hydraulic assist. Could that be the problem? At the moment ,when looking at the linkage ,it appears to move the pressure plate when the clutch is depressed.