Dear Erik:
--Have you ever tried DeoxIT D100L?
--I, as well, use the high purity isopropyl, with good results. Also, I have used CRC Electra-Motive Electric Parts Cleaner, followed by compressed air. It evaporates very quickly and is non-flammable, but be sure your area is well ventilated. If all else fails, you might consider trying DeoxIT D100L, if you can apply it without getting it on the wafers (especially those effing phenolic ones). I have had satisfactory results with it.
--Apply very sparingly, rotate the switch periodically over the course of an hour or two, then clean with isopropyl. Apply DeoxIT Gold, or DeoxIT Shield to preserve. If that does not do it you may have to try the pencil eraser trick. I have even used the striker from a book of matches, to slide between the contacts, as with the old automotive points. Someone on this forum said there is a special tool to do this, but I cannot find the post.
--I regularly use this stuff on recalcitrant USB and SATA cable jacks with good results. I also use it on my DMM probes' banana jacks whenever the parasitic resistance increases above 0.15 Ohms or so.
--Let me be very clear. The DeoxIT solution is only for "no go" and or intermittants do to dirt and grime, and light oxidation. It will not, needless to say, cure mechanical problems. I only mention this because, the last time I recommended this stuff, someone quoted me, and a person who has my posts set on ignore, rang in and accused me of recommending "magic goop". Then somebody accused me of waving a dead squirrel at the problem. So whatever you do, do not quote the first sentence of the post, unless you want a laugh.
--Once upon a time, I had a multiple wafer switch with a "no go" problem. I tried all of the above, but still no joy. So, after taking a lot of pictures and making notes. I removed the switch for closer inspection and, proceeded to check every set of contacts with a voltmeter (desoldering components as necessary). Finally, I found a contact on one of the wafers that had an almost invisible break in it. I managed to close the break with solder, and Bobs your uncle. Do not give up! There are already enough shelf queens about.
"But leave the Wise to wrangle, and with me
The Quarrel of the Universe let be:
And, in some corner of the Hubbub couch'd,
Make Game of that which makes as much of Thee.
"Omar Khyayyam" 1048 1131
Best Regards
Clear Ether