Well it certainly looks a bit of a mess! Corrosion is always a result of moisture and I can only conclude that these units have lived in an environment of high humidity that has led to condensation. Maybe in the flow of an aircon that has cooled the units thus causing the condensation.

Having said that the damage is mostly cosmetic and as many of the pots have associated switches, direct replacements might not be easy to procure. The first thing I would do is to spray all the mechanical parts (switches and pots) with a high quality switch cleaner and lubricant. Make sure to get the spray right into the pots - there are usually small holes or slots in these that you can coax the spray into. Do NOT use WD40!

If this removes the clicks and crackles when operating the pots and switches then nothing is too far amiss electronically. Be sure to give all controls a "workout" to get the cleaner right into the "action".

It would then be up to you to decide whether, for cosmetic reasons, that you would take a wire brush to the rust to clean things up a little.

Thank you for the input. Someone else had mentioned on GS that it could possibly have been salt air damage...perhaps they were near salt water/humidity for a while?

I agree that it is cosmetic at this point and I have already used Caig deoxit and lube and flushed out the pots. My concern now is keeping things from progressing and getting worse. I have considered cleaning the outsides of them but I am afraid of getting rust particles inside on the wipers. I have also thought about removing the switch/pot assembly and then dismantling the pot casing and cleaning it off. I have done that on old guitar pots, but I am not sure if that would work at all in this situation. I am going to throw some desiccant/Silica Gel packets in their for good measure. Still thinking it through!

Surely if your Buddy had these from new, he is going to know their history? With corrosion like that it seems more than just a trip to the seaside (unless they went swimming!) and I suspect they have been in a sustained condensing atmosphere for most of their life.

Removing the corrosion is not going to be easy but maybe tackle it a different way. Further corrosion is going to need more moisture so you could try thoroughly drying everything and then painting on some clear lacquer (don't spray - it could get everywhere!). This should prevent further damage or at least slow things down. It's essential though not to trap any moisture under the lacquer.

Unless the unit is hermetically sealed, dessicants are going to do very little, even if you dry them out every week or two. This applies to virtually any environment. In the marine industry many things are lacquered and/or very well sealed to protect against corrosion. When properly sealed, many units do not use dessicants but are rather purged with dry nitrogen when sealing.

The last things I saw that looked that corroded inside were literally submerged in salt water for days at a guys beach-house during/and post-hurricane. Then they let these amps and instruments sit around for years with no attention. By the time I got ahold of them all the pots and switches were seized up and needed replaced. Luckily they were readily available.