I have a Toro proline with a 12.5 Kaw engine and a peerless 700 series transmission. The left belt has started to roll itself off the the drive wheel. The cause....the the spline coming out of the transmission is sliding to the extreem left (about 1.5") resulting in the pullies not being aligned. I can push the spline back in towards the transmission with a screw driver but is slides back out after traveling about ten feet. Is there a simple fix for this? Do I need to replace parts? Thanks for any help.