Ice on Fridge Freezer Floor

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?
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Hi,

The serial # will help with that... http://www.applianceaid.com/appliance_age.html

Certainly sounds like the defrost drain is clogged or restricted.

It does, behind the back wall in the freezer is where it starts.
http://www.applianceaid.com/frig_leaking.html Some helps and tips.

Yes there is...you can see a pic of it from below... http://www.repairclinic.com/referral.asp?R 3&Nf5946
jeff. Appliance Repair Aid http://www.applianceaid.com /
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