Take a look at this Impedance selector switch. Not sure what to make of these terminals?

[Helmholtz]

Looking at the picture, I don't think there is a problem with the switch at all. The contact area looks shiny and like others said, all it might need is a little Kontakt 60 (followed by Kontakt 61) or Deoxit applied with a Q-Tip and a few turns to wipe the contacts.

[g1]

Somebody gave me a can of this stuff, it's lanolin based and gets very viscous. Maybe similar to what is being described.
https://www.fluid-film.com/

[Helmholtz]

Somebody gave me a can of this stuff, it's lanolin based and gets very viscous. Maybe similar to what is being described.
https://www.fluid-film.com/

Lanolin is wool wax and I don't think you want it on high current contacts.

[Mick Bailey]

I use something similar called Tectyl to prevent winter salt corrosion on cars and bikes, and some other outdoor stuff prone to rain exposure or workshop equipment subject to condensation.

[Enzo]

I agree with Helm, the contacts look OK. I consider them self cleaning. All that tarnishing where the contacts don't rub? Who cares, they are not contact surfaces touching.

I worked in the coin-op amusements industry a long while, and back in the old days, when pinball machines were full of a ton of relays and stepper units with brass feeler contacts, we might put a thin film of light grease on the wiper discs to reduce wear, but otherwise they tended to keep themselves clean by rubbing. In fact in relays, there is something called "scrub". As contacts just close, they touch at some point on their surfaces. As the contacts continue to close tighter, the individual contact points slide slightly across one another. That is called scrub, and tends to self-clean the contacts. I did have to burnish relay contacts now and then, but it was from arc pitting, not dirt.

[Chuck H]

I agree with Helm, the contacts look OK. I consider them self cleaning. All that tarnishing where the contacts don't rub? Who cares, they are not contact surfaces touching.

I'm cool with that, with one caveat. It's an impedance switch. There's a good chance under many circumstances that it could be left in one position for a very, very long time and the unused contacts could develop their maximum oxide thickness. Maybe it'll scrub right off by switching? Some reports say it can be a problem. In this particular case, being an impedance switch, that would leave the output unloaded (= bad). I did read that this oxide layer tends to be less of a problem in higher voltage circuits.?. But an impedance switch in a low voltage circuit.

I'm just saying that a cleaning and a little electrical grease on the contacts to keep them from oxygen is probably a lesser evil than whatever debris might collect on the grease.

JM2C

[SoulFetish]

Looking at the picture, I don't think there is a problem with the switch at all. The contact area looks shiny and like others said, all it might need is a little Kontakt 60 (followed by Kontakt 61) or Deoxit applied with a Q-Tip and a few turns to wipe the contacts.

The contact area in the middle terminal (8Ω selection) is the switch position that was and is normally in. It was not cleaned by the switching action, nor did deoxit remove the discoloration. I don't think that the switch contact to the right looks very good at all.

I would have to agree with Chuck on his point. If this was a switching jack in the signal chain, or a relay, I could chalk it up to a nuisance probably. But the fact that the full output goes through this switch, the condition increases contact resistance, which increases heat–which worsens the tarnish–compounding the contact heating, etc. This could lead to a switch failure and potentially cause costly damage to the amplifier.

My point here is that silver plated open air contacts, supplied or left untreated seems lazy or negligent on behalf of the Manufacturer. It does not take long for silver to tarnish, and the technical paper I posted above articulates the the mode of failure, and provides some good examples of preventative measures.
In situations where untreated silver plating is used In critical locations, it's my opinion that taking some of these simple measures is the wise choice.

[Helmholtz]

From the paper:

"Sealing out corrosive gases can help to protect metal surfaces against atmosphericcorrosion. Corrosion inhibitors/lubricants applied at any sliding contact points andsurfaces will do this job very well. Special attention should be given to the correct choiceof these products to not induce interference with electrical properties of conductive parts.Effective lubricant for electrical parts should be chemically inert towards the metalsurfaces to be lubricated. Lubricants used on silver-plated surfaces should not carrysulfur-containing compounds. Lubricants for electrical parts should not collect dust and particulate matter, should beresistant to oxidation and chemically inert to corrosive atmospheric components. Theselubricants should not build non-conductive deposits on contact surfaces after multipleoperations and retain long-term thermal stability at least up to 400 oF. Any corrosioninhibitor must be thoroughly tested for electrical application."

Not everything that works for car battery poles (extreme contact pressure) is suitable in electronics. I am not sure if (non-conductive and sticky) grease is suitable for every high current switch.

I doubt that the performance of the switch shown could be improved by any contact grease. OTOH Kontakt 61 applied after cleaning with Kontakt 60 or Deoxit will leave a non-sticky protective film.

In case of doubt I would ask a major switch manufacturer.