I have a 2005 BX23 that I use a few (5) times per year to mow my hillside. I haven't used it for about a year and when I went to use it the PTO clutch lever was stuck. I removed the ROPS and the fenders and was able to knock on the PTO clutch arm to break it loose. I can now operate the PTO clutch lever but the PTO clutch still doesn't engage. Is the PTO clutch piston jammed or what could be the problem ?