Could you try this?
Pour two cups of vinegar or lemon juice into the tub, and run the washing machine through a complete cycle on the hottest setting to remove odors, stains and detergent build up.

Every now and then I was running through a vinegar wash on my previous washing machine. My current one has a self clean cycle - basically a hot wash/soak (with a couple of scoops of detergent) cycle so I haven't done the vinegar wash in this machine.