Hello,have you tried adjusting the traction cable? If that doesn't help clamp the fuel line and tilt forward and rest on the bucket.Remove the lower access panel to inspect the rubber drive disk and springs.Have someone squeeze the drive cable while you check movement of parts.
Do you still have your operators manual? If not ,here is a link where you can download it.It has some info for adjusting or replacing belts. https://groundscare.custhelp.com/app/answers/detail/a_id/972