One option is to adopt a Motolita as a replacement (keep the old one for potential sale with the car).
https://www.moto-lita.co.uk/Our S2 wheel has a similar "patina" that is annoying and I have always preferred all leather or suede/ette
I believe that PeterJ found a very good leather upholstery lady down his way (Salisbury) who would probably be able to do it based on her posts on FB in the past. I believe it is this lady
https://www.facebook.com/profile.php?id=100063439974639
