After a couple of years of use, all of a sudden my front load washer is smelling musty. I read on another website that especially if you use liquid detergent, the detergent can build up in the washer. They recommended using Cascade Complete dishwasher detergent to get rid of the build up. I'm not sure what it is about Cascade Complete, something about breaking down the enzymes, but it has to be that specific type/brand...
Anyway, I tried it and I could not believe the gunk that came out of my washing machine. I ran 5 empty cycles of Cascade Complete with hot water, and there were tiny little dirty globules of ...stuff... that came out. Before I tried washing the machine, I couldn't see any dirt or build-up anywhere on the washer (only a musty smell), but it must have been lurking somewhere inside. I was totally shocked, it was just gross.
I just tried this a couple days ago, so I don't know if it has completely solved my musty-smelling washer issue, but after seeing all of the crap that was lurking in the washer, I know it certainly didn't hurt.
FWIW, my washer isn't known for having mildew issues, and I do leave the door open when not in use. I also think that the large amount of iron we have in our well water can't be helping either.