How black marks get inside a closed dryer has always been a mystery, at least to me.
Given that you had what sounds like roller noise, it may be that your rollers are disintegrating and that the debris is getting inside the dryer and despositing itself on your clothes. The uniform marks could come from the tumbling nature of the drum.
I would replace the rollers, front seal and drum bearings. These are all inexpensive and should be done on a dryer your age anyway. Hopefully that will solve the problem.