Interior of fridge is not dry. Most items in fridge have moisture on them like when you pull a cold bottle of pop from the fridge and leave it out on the kitchen counter it slowly sweats and develops moisture on the outside of the bottle - inside of fridge is like that all the time and moisture develops on all bottles, tubs, and surfaces inside the fridge (cheese goes mouldy very quickly; paper labels on bottles eventually develop black mould, mould grows in cracks and crevices throughout fridge interior). Otherwise fridge runs fine (cold enough, no blocked drainage tubes, no water pools in bottom, freezer working perfectly). The "freon" (or whatever they are using these days as a coolant) has been topped-up and the rubber seal/gasket around the fridge door has already been replaced - but the problem persists. Fridge is a side-by-side Sub-zero, purchased new in 1989. Hoping not to have to replace fridge as it is built in to kitchen with matching panel to cupboards. Any possible solutions?

Your fridge is 27 years old ! I can't imagine what the freezer is like. And you are eating food out of this appliance which should have been replaced years ago !

First idea would be that they have a drain, that often gets clogged, and needs to be cleaned out.

The other is that the rubber seal is still not making a good seal.

With that said, I will agree, that unit needed to be replaced years ago.

You need to take it outside and wash it out. Remove the cover to the freezer coils and remove the rear cover. Wash out the condenser and the freezer (evaporator) coils and clean the drains. Clean all fan blades and oil the motors, too. Replace all covers.

I hear this and think that it's not sealed properly I'm guessing it's a problem with the seal. I know you said it wasn't, but obviously you're not an expert on fridges otherwise you wouldn't be asking about this.

I'm not an expert on fridges either, but I've had this issue, and it was the seal on the fridge.

You really need a new fridge. Look on eBay, or if you have it, Kijiji. I've had my last 2 fridges from Kijiji. Free. No, they didn't last long, but they worked with no issues until they died, and then a new one, for free! They aren't fancy, but they worked.

I think it's time to put this baby to rest.