My approx. 10-12 yr old Whirlpool DU8500XX started leaking massively from front door. After much head-scratching...(drain not clogged, door gasket OK...) I noticed the plastic air vent at top left, inside of door seemed to have a little crud visible through the vent slots.
Popping the plastic out, with a knife blade, as there are no external tabs to facilitate removal, I found something like a grease trap, which was blocked with crud. Removed crud, problem solved...I guess for another 10-12 years at the rate we use the machine. Your mileage may vary.
Note: This plastic door had no message on it "Clean this trap at regular intervals." And was not obviously a maint. point.
I told a friend about this and he said it's the manufacturers means of causing the unit to fail after you've had it "long enough". Most people will say: "Well I guess it's time for a new one." Darn few will figure out the trick. Most people will buy a new one.
Thanks, Whirlpool! I wonder if other manufacturers have similar features?