Our refrigerator (freezer-on-top, GE "No Frost", c 1980) has suddenly
started producing large amounts of water along the underside of the
freezer door - possibly only at the 'open' corner. Both the freezer and
refrigerator are still working. I find no icing on the freezer
walls/floor, and the floor does not seem wet.

From other reading, I'm guessing that this is due to a stoppage in the
freezer drain. Would that be a good guess?

And, before I go to the trouble of looking for that, is there anything
else that might cause this condition?

Thanks,
George