wdt780saem1. problem started a few months ago. there is a very fine brown/black dust evenly coating the inside of the washer and on dishes.
upstream - i have checked the water coming into the washer. all wipes come back clean. i feel relatively confident it is not an iron problem. we are on city water and see no evidence of iron problems in any other areas/appliances. if it were iron, all residents would be having this problem.
downstream - i have checked drainage. there does not appear to be anything regurgitating back into the washer. the drain line is opaque and i don't see any obstructions. the valve appears to be working correctly. i have removed and inspected drain pump. all clean
that leaves something in the washer itself. i see no evidence of worn/compromised parts. i removed main pump. all wipes come back clean. heating element is clean. i have cleaned all parts inside several times. all wipes inside tubing/wash arms come back clean. it is something happening after the water is sprayed and before it drains. we have run numerous cycles with dishwasher cleaners and no dishes. there has been no metal such as cookie sheets.
i am absolutely baffled. this dust/residue/film appears to be coming from nowhere. it costs $100 just for someone to step into our kitchen. then labor and parts. we can almost buy a new one for that much. i am troubleshooting the problem because i feel like it can be solved relatively easily if the root cause can be found.