This is from Mustang's website support section, might be worth a shot.
Cuts, Scratches or Scuff Marks
As with any upholstered product (such as couches, chairs or car seats), there is a possibility of cutting or tearing the cover material. Please contact Mustang directly and one of our seats experts will provide you with the best possible advice about your particular situation. (Most local upholstery shops do a very good job of repairing vinyl.)
If your seat has been scratched or scuffed, try gently applying a small dab of black paste shoe polish on the affected area. Allow it to dry completely, then buff out with a clean soft cloth. If you have any questions, please contact Mustang and speak to one of our seat experts.