We have a Maytag MZD2766GES side by side refrigerator. Stainless steel
front, ice/water dispenser in the freezer door, filter. Looks good, came
with the house, don't know the age.

Works well, but recently a sheet of ice has been forming on the bottom of
the freezer. The freezer bottom slopes from back to front, and the ice seems
to start at the back and each day extends nearer the front. After 3 days it
is almost to the door.

Initial guess is that the defrost drain tube might be clogged, but I this
beast does not seem to have such a thing. There is nothing in the manual
about a drain or keeping it clean and I can't find anything on the internet.
There is no evaporation tray below the fridge and I can see anything in the
freezer compartment to disperse water. So when it defrosts, where does the
water go?

Any idea what might be causing the ice and how can it be fixed?