Why are black blobs, bits and streaks left on my wash?

When I wash clothes in my Bosch WFF 1401 with a hotter wash, they come out with black bits on them. I wipe down around the grey, rubber front seal after every wash. It is 'stained' black in parts. It's been doing this for a while and I find other Bosch users are now complaining. How can I cure this?