Grey marks on washing

Washing machine is bosch classixx 6 1400 express

The problem occurs most noticeably on a white wash where grey blackish streaks appear on items. Can be on bedsheets or even smaller items of clothing, like my 3 yo daughters vests.

Initially thought the problem was the tumble dryer but an engineer visited and explained it was the washing machine. He was only servicing the dryer and not the washer. He suggested an empty wash on hottest temp with a cleaner. So I’ve tried this several times but recently noticed that it’s getting worse.

I’m at the point of just getting a new washer! But thought it’s worth asking to see if there’s anything else we could do.

Thanks in advance
Linsey