Nearly every aftermarket shock uses polyurethane bushings. These last a lot longer and deflect less than rubber, and they are generally impervious to oil. Some have steel inserts (right). With the insert, you can tighten the shock bolt to 65-85 lb-ft. Without the sleeve, you will want to use a Nylock nut and don’t tighten the mounting bolt so much that it compresses the bushing.