I've been having problems with dirty marks on my washing for a while now but it has got a lot worse today. I do regular hot washes and use citric acid or soda crystals every now and then. The dirt seems to be coming from the join at the back of the drum, see photos. Any ideas? It mostly happens with dark washes which I am possibly prone to overloading so I will try to put less in. I had an engineer round for the dishwasher who said the bearing are fine so it shouldn't be that.