Well this was an easy one. I removed the rear interior panel of the freezer section, exposed the coils and the drip tray. Sure enough, the drip tray and drain tube were filled with ice. I used a hair dryer to thaw the drip tray, used a big towel to soak up the water, then used a turkey baster loaded with hot water to heat the drain tube. I let the hot water sit for a minute, then soaked it up, and repeated the process until the drain opened up. My guess is that the freezer door was not shut properly for a long period of time - possibly too much stuff in the freezer. It's was easy to see how the water would overflow into the fridge section. Just saved a bunch of dough on a service call - woohoo !