My frigidaire dishwasher has been giving me issues for the last while. It worked fine for a couple years, but then started acting up by the dishes not drying. I replaced the heating element, but that did not solve the issue, so I just lived with wet dishes. Now, the top rack does not wash the dishes well anymore and I get a black mildew on the inside of the tub and inside of the door. I took a couple hours one day about a month ago and took it apart and cleaned below the bottom rack and got quite a bit of gunk out of there, most of it black. EWW. No noticeable difference after the cleaning.
I use Cascade Complete pods, a rinse aid, and I did do a vinegar/baking soda cleaning cycle recently too which did not help. I almost bought a used dishwasher today and came to my senses that I could be just buying a whole 'nother set of problems, so decided I should just fix the one I have (if possible). I used to wash with dishes on the bottom and glasses and tall utensils on the top - now I have to wash the glasses on the bottom. I have noticed a white residue on some dishes like pots/pans especially and plastic containers, so I end up rewashing those by hand.
The black mildew/staining on the tub and inside of the door has me mostly worried (and it is a major PIA to continually clean this thing!)