Okay you need a toothbrush (old one lol) and some of that thick bleach you use in the loo. wear gloves and old clothes as the stuff will spatter. Pour some bleach into the seal and give it a good scrub round with the toothbrush. leave it a few minutes, wipe with kitchen paper and repeat. Put some more of the bleach into the detergent dispenser and run the machine on the longest hottest wash you can. When the wash has finished, check the seal which should now be clean, if it isn't repeat the process. Once the seal is clean,run a long cold cycle before you put anything in the machine then wash something that wont matter if it gets bleached.