I had the same issue with an XL bar a little while back, it turned out that the belts were so old that they began to dry out and where they passed over a sprocket they took that shape from sitting so long. When the bar was then powered up and run it appeared to slow down when those curved areas passed between the sprockets as they would not flex and straighten. Once I put new belts on that we're more pliable the issue went away.Like TDC said, WD-40 is good to free something, but once it is freed, you need some lube in there to keep it going.