GE Monogram fridge leaking defrost water

I have a 1988 GE Monogram 42" side-by-side fridge (compressor on top, model BISW42EKC) that has water pooling on the inside bottom of the refrigerator side. The water appears suddenly, and is probably related to self defrost.
The GE hotline indicates it's probably a plugged drain line, but won't give further information.
Anyone know how to access the drain line in this model? I've worked on other appliances and would prefer to avoid a service call if at all possible.
Thanks, -Lance (remove ZAPSPAM to email a reply)

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