I wanted to let you know, IPA method isn't absolutely safe either. IPA itself is relatively safe but what is often sold as IPA from regular stores are de-natured. They are often mixed with numerous things including gasoline. (often labeled as 70%) You can try cleaning mirrors and let it dry. You can often see oily residues. So be careful. In United States, if you look hard enough, you can find 90% kind. 99% is also available. (even from places like Amazon!) They are safer from de-naturing prospective. I have only seen 100% from chemistry supply stores. I have 70% and 99% and use them depending on what exactly I am doing.
I use De-oxit as well, but with some care. Sometimes spray some into a container and use syringes (I have lots... I am diabetic) to apply precisely. De-oxit spray has very bad tendency to spray all over the place. I had varying degree of success. So far, I haven't had any case it caused damage.
There's really no 100% sure way of dealing with old switches. I think, the best you can do is be familiar with various methods, and use small amount first.
While cheap IPA rubbing alcohol may have contaminants, it’s probably not denaturing agents, because IPA is itself a denaturing agent. Only ethanol (the alcohol we can drink) needs denaturing, which is the addition of a nondrinkable adulterant for tax purposes. IPA isn’t drinkable anyway, so it doesn’t need to be denatured.
According to various medical and addiction treatment websites, IPA rubbing alcohols
supposedly contain Bitrex to make them unappealing for accidental ingestion, but I frankly don’t believe it, because Bitrex residue gets
everywhere and you taste it on everything, even after thorough hand washing. (I’ve bought ethanol fireplace fuel with Bitrex before, not realizing it did, and I couldn’t use it for cleaning because it contaminated the whole damned house with Bitrex.) And for sure those sites are just plain wrong in talking about “denatured IPA”, per above.