I can't belive this has popped into the threads.
I complained to my other half for months when I got back from Offshore, and first got in the SQ5 car after being away for 3 weeks and she picked me up from airport.
I was so,
so sure it was due to her rings until I actually found out it was myself causing this, after months of thinking it was her (I apologised)
It's when you get in / out the car, you are rubbing off the steering bottom part of the wheel with either your jeans or part of clothing.
Try carefully getting in and out for the next week or so, and you will notice it never happens again