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Here is Larry's info:
If your leather or vinyl has scuffmarks, scratches or areas that the surface color has been removed, you may refinish it yourself. Most German seats are famous for scuffing on the left bolster of the driver's seat. This is usually caused by your belt loops as you get in and out of the seat. The key is another Surflex product. The Surflex Colorant & Finish for Flexible Surfaces may be matched to the exact color required. Any interior leather or vinyl surface may be refinished. It is not recommended to spot finish any area. If your seat bolsters have belt loop scuff marks, you should refinish the entire front of the seat. I usually do from welting to welting. This provides a visual break that does not make the non-refinished areas appear quite as shabby. But then why not do the whole seat, dash, or door panel? Start by conditioning the leather to insure that the leather is fully hydrated with oils. Once the leather is fully conditioned or softened, if needed, then clean the area(s) to be refinished with a suitable Organic Solvent. I prefer P21S Total Auto Wash or Wurth Citrus Degreaser. Prior to usage, test all solvents on an area that does not show. I use the excess on the underside of the seat to test the colorfastness of the finish. Spray the solvent on a soft lint free cloth, and then wipe down the surface(s). Repeat after a few minutes. Rinse several times with a sponge or cloth and a couple of buckets of clear water and allow to dry thoroughly (at least 24 hours). The manufacturer of Surflex says to strip the old finish off using lacquer thinner, commercial paint remover or C-P Stripper. I don't, because most interiors are not in that bad a shape and I have never found it necessary (They also recommend lightly sanding the area prior to usage, I don't do that either - no guts). Mix the Surflex completely and apply with brush, spray it on or use it like a wood stain. I prefer to use a small piece of lint free cloth and work the Surflex into the leather or vinyl just as if I were staining wood. Once the desired color of finish is achieved, allow to dry undisturbed for at least 24 hours. I allow the surface to "harden off" for about 6 weeks before applying any conditioners to leather or vinyl protectants to vinyl parts. I have not had a lot of luck refinishing dark leather to a significantly lighter color. The old color tends to show through in small "cracks" and the whole panel seems to be "muddy". Maybe if you strip off all the old finish, it would look better. Someday, I will get an old seat and give it a try.
The Surflex Black Colorant works great on black bumpers, black spoilers or black rubber/vinyl trim that has been severely scratched or badly scuffed and is beyond the help of Black Again. Clean the entire part thoroughly with P21S Total Auto Wash or Wurth Citrus Degreaser, rinse and dry thoroughly. Mask off the paint and then stain the area with the Colorant and allow to dry. It will look like new. After about 3 weeks hardening off, coat with a protective coating of Black Again or One Grand Exterior Rubber.
Small cuts, cracks or holes in leather may be partially repaired using another Surflex product called Flex-Fill. This is a semi-flexible cosmetic filling material. You use it like a Spackle compound. It will take the Surflex colorant similar to leather or vinyl. I have been able to repair several damaged areas and hide them so they are not visible to the casual observer. Will it make a three-inch crack in your dash look like new? No, but it may help hide it so that it isn't quite so obvious. I have found that forcing Flex-Fill under the repaired area and forming an inverted T patch works best. Once the patch is dry, sand lightly to blend in with the leather or vinyl. Clean the area thoroughly and refinish with the Surflex Colorant. This is a learned skill, so you should practice on a test piece of leather or vinyl. Perfect your techniques before you tackle your expensive interior.