Fridge 101 - In modern fridges with automatic defrosting, on a regular basis (often every 8 hours) a heater comes on for a short time, melting the frost buildup on the coils in the freezer. The water then runs down to a tray, down a tube (usually down the back of the fridge) and into the evaporation pan at the bottom. This pan sits among the fan and the condenser coils (which are hot when in operation) so the water is quickly evaporated.
I checked online and it turns out that this pan is no longer available (it's a 20 year old fridge). I came up with a plan to repair the pan. First I used an abrasive wheel to clean the rusty bottom of the pan:
My plan was to plug the hole with tape and then use a spray-on rubber coating to seal it. However, the hole was way too big, but I decided that the long bit of the tray only goes out under the heating coils to improve evaporation; the coils are hot and so should never be dripping water. So I cut it off, made two cuts and folded it up. I then put on about 8 coats of rubber lining (most of a can) over the course of a couple of days and reinstalled it.
I also installed a water alarm behind the fridge to monitor for further problems, especially since we're having hardwood floors installed in a few weeks.
I have an alternative plan in case this fails - I have a simple way that I thought up to form metal in to the shape of the pan.