A few questions on seat belts from the rear of my 68 Cutlass Convert. Can these be cleaned with anything to restore them and can the plastic covers be removed / taken apart? The belts are very dirty but otherwise look solid. I.E. no fraying or cuts, they function fine and the buckle covers are in good shape. How expensive is getting new belt material put on my hardware? I am not looking to do a full technically correct resto but would like to salvage these if it is possible. Thanks.