Use Hydrogen peroxide...works like a charm on many things around the house.
You should have left the washer door open until the interior of the washer is completely dry before shutting the washer door.
This seal should have a small drain built into it at the very bottom. It often gets plugged with lint and slime, but can usually be cleared out with a pipe cleaner. As far as removing the mold, have you tried white vinegar?
Usually answered in minutes!