Start with the easy things;
I had a front loader for several years and it never went smelly, we even lived in Townsville where everything else got a nice layer of mold on it, but the machine was fine.
When not in use we would leave the door unlatched and the hose was at a good height so there was minimal water washing back into the machine after the pump stopped. Instead of having it dump down the side of the laundry tub, you could try hooking it up to one of those barbed fittings on the 'S' bend, that way the pump has less head to push the water against.
Have you pulled the lint filter out and cleaned any hair/lint/gunk out of that?
Run it through a hot wash with a triple dose of nappy sanitiser?
The Bendix machine we had you could take the back cover off the box, remove the drive belt and then undo the clamp on the drum to get right into the space between the drum and the water proof outer bit. You might have a small piece of cloth stuck in there that is moldy.
I had to strip the machine after the concrete weight on top of the drum broke lose and it flogged it's self to death and split the drum

, not due to smells.