A Miele dealer here advises to do a boil wash with two dishwasher tablets now and then. It might be a bit stronger than just citric acid.
Somehow it should stop releasing those solids. I think the previous owner didn't use enough detergent.
BTW, have you checked the hose from the detergent dispenser and the dispenser housing to the drum to see if there is any mold in there? Take the dispenser out and look inside. For the hose, use a bottle brush or so and some water. If there is mold in there, you could try cleaning it with toilet cleaner.
Somehow it should stop releasing those solids. I think the previous owner didn't use enough detergent.
BTW, have you checked the hose from the detergent dispenser and the dispenser housing to the drum to see if there is any mold in there? Take the dispenser out and look inside. For the hose, use a bottle brush or so and some water. If there is mold in there, you could try cleaning it with toilet cleaner.
