First check that there's nothing stuck in the filter trap, usually on the front of the machine at the bottom.
Next, down to the pound shop for a couple of bags of soda crystals (NOT caustic soda), put some crystals in the soap dispenser and the rest in the drum. Run the machine, empty, on the hottest wash then check. If the guff's still there repeat and that should do it.
When the smell's gone, leave the door ajar every time after use to allow air circulation.
I do that once a month now and no problems.
Good luck.