Question about cleaning rubber window trim

When cleaning the rubber trim on the exterior of the windows.. Is it normal for there to be never ending black soot coming off on my towel? Should 1 continue until there's no more black coming off? Or am I destroying the rubber? Stupid question, I know, but I had to ask.

Thanks.

All cleaned & coated.

This is what they looked like before:

View attachment 40443

After:

View attachment 40444