This typewriter was quite grimy, so I removed the shell (fairly challenging) and gave it a bath in an ultrasonic cleaning tank. Mitch Hamm alerted me that such tanks, big enough to dip a portable while keeping its keys out of the water, are now available for a mere $150 or so. Here’s the Royal undergoing what sounds like electroshock therapy, but is really just a micro-agitated bath. Concentrated Simple Green Industrial Cleaner & Degreaser was added to hot water in a 1:20 ratio.

Old school repair guys used a lot of different stuff that's no longer available due to being... Not good. Ha. But naphta was one that's still widely available as white gas aka "coleman/camping fuel" Essentially naphtha with stabilizers to keep it from going bad. Mineral spirits works as well, but naphtha leaves less residue in my experience. Lacquer thinner is good for especially stubborn crap and cleaning slugs, but evaporates really fast and the fumes are no bueno. Alternatively; non toxic degreasing cleaners like simple green are usually my preferred method of cleaning up especially gross machines. Typically very safe on paint finishes and internals, just make sure to keep it off the decals. (It can and WILL erase them if it sits for more than 10 secs) Really though, nothing beats air and a long handled "paint" brush. My air compressor and blow out tube are some of my most cherished tools.