My son's Dart already has a sure grip, but yesterday we discovered that it may not be working properly. We were working on the hydraulic clutch and wanted to make sure the clutch was disengaging. With the trans in first and clutch out he could spin one side and the other side was spinning opposite indicating that the SG may be worn out. Dr Diff has a clutch pack for $117. Is that likely all we'll need? How difficult is the rebuild?