I had the same problem and I fixed it fairly easily in about 45 minutes:
The root-cause is the incredibly stupid design of the plastic ring that snaps over the plastic wash tub. It is filled with many nooks and crannies that rarely contact the wash water, thus getting scummed up and moldy. See a picture of the gross mess here: http://www.falselaborblog.com/2008/08/moldy-maytag.html
The fix involves opening the top (easy) and removing the ring (fairly easy) and can be done yourself if you are the least bit handy.
Unplug the unit.
***If you are mold-sensitive, wear gloves and breathing apparatus or have someone do this for you.***
Tape the lid shut so it doesn't flop open when you raise the lid.
Use a putty knife to push into the front seam about 1 1/2 inch from each corner. This unlocks the top and it will open just like the hood on a car. Carefully secure this in the open position and don't let it fall on your head or your hands.
You will see plastic fasteners holding the top ring around the outer plastic wash tub. These will unsnap (you may need a flat-head screwdriver for some of them).
Carefully lift this out and try not to puke when you look at the underside (see photo http://www.falselaborblog.com/2008/08/moldy-maytag.html
). Take it to a laundry tub or bathtub and thoroughly clean it by scrubbing with hot water, detergent and bleach.
Before replacing the ring, use a thin brush to clean between the upper part of the wash tub and drum---the scum and mold will be in here also.
Replace the ring in the reverse of the above steps.
Prevention: There is none. You will have to do this every 4 to 6 months to prevent mold from infesting all of your clothing, etc.
I'm experimenting with limiting wash load size to "large" and never using "super", reserving the "super" setting for running periodic (hot water + Clorox) to see if it reaches the idiotic upper ring and keeps it clean. I am not hopeful that this will eliminate the need for these overhauls.
P.S.: The person that designed this washer should have all of his/her underwear and bed linens washed in an uncleaned Maytag Atlantis for life.