When I go to engage the PTO, sometimes it doesn't fully engage the clutch to turn the blades. It has happened to me 3 times in the last couple weeks. I have to disengage and then do it again and it works fine. Anyone have this happen, what could be the problem? Is the clutch going out? I always engage/disengage at half throttle and this mower only has 700hrs on it. 2004 Lazer 52 w/23hp kohler.