Silver sulfides on rotary switches

Which product is best for cleaning heavy "tarnish" on silver plated switch contacts?

Many of these are not accessible for "mechanical" cleaning with a brush or pipe cleaner. I've been repairing electronics professionally for 30+ years, and have run into the problem of "dirty or noisy" rotary switches. Sometimes based on the success or failure of various cleaners/deoxidizers, the "standard cleaning procedures" as referenced in the CAIG literature, works.

But, there are times when the old standards just don't work, and a closer inspection shows a really black and stubbornly adhered "tarnish" on the silver, which I can only guess is silver sulfide. This can render expensive test instruments completely unusable, and I have no recourse but to replace either the switch (often impossible) or the whole instrument (expensive, we are not talking $5 radios).

I have used DeoxIT® and Cramolin in the past, but even they won't always work in these sorts of situations, so I was wondering if any of the new formulas would be more effective.
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You might try the CaiKleen TNX. It comes in a kit, and the contents include:

CaiKleen TNX, (to clean)
CaiKleen IPA, (to flush);
DeoxIT® GOLD (to protect);
Lint-free accessories;
Safety goggles with complete instructions.

It would also be a good idea to have some "canned" (compressed) air available for your project, as well as gloves.

Since the CaiKleen TNX is water based, you must remove it completely, as directed.

NOTE:
DeoxIT® GOLD (formerly ProGold)
DeoxIT® GOLD GxL (formerly ProGold GxL)
DeoxIT® SHIELD (formerly PreservIT)
DeoxIT® FaderLube (formerly CaiLube MCL)
DeoxIT® FaderGrease (formerly CaiLube MCL P20 & P40)
DeoxIT® Grease Type M260 & L260 Paste (formerly CaiLube Grease).