I have a challenger MT 255 compact tractor with front loader I purchased new around 2004. Recently, the tractor bucket lifted on it's own after I finished mowing my property. I got off the tractor with the engine running and was going to blow off the grass clippings from the finish mower, and to my surprise I looked and saw the boom lifting. I quickly tried to let it down but the lever was firm and would not push forward to lower the bucket. I killed the tractor and let it cool for about 20 minutes and attempted to let it down with the engine off and it went down slowly. I cranked the engine up to put it in the shop and the bucket is working but very sluggish on the downward position and no downward force which normally will lift my front wheels. Anyone have any ideas as to what would cause this?