My church has a John Deere L 111A , serial # GXL111A086103 and it keeps throwing the blade belt. I replaced the belt 15 months ago. Rider has a manual engagement for the belt and with it off the belt seems very loose to me. Even when it is on, seems loose to me. They tell me it throws the belt when they are cutting the grass. Would a belt stretch much in 15 months? I don't see any way to adjust the tension on the belt.