just about every machine will run into this.....
about the only place food/slime will build up is right at the bottom of the door, where it goes into the tub as you close the door....its one area that doesn't always get flushed enough....
never hurts every now and then to take a scrungy sponge or toothbrush and run it along that area....
I just checked mine today, it looked clean, until I ran my fingers underneath and pulled out the grunge...