I use denatured alcohol for the slots. I am not saying it is the best--a lot of people prefer and recommend mineral spirits--but it is currently my personal preference.
 

Uwe wrote:

Why is PB Blaster even on the list, and who voted it?  PB Blaster is a penetrating oil not unlike WD-40, so unless it's an extreme case of a rusted typebar seized within the segment you should never have that stuff near those components. 

And this is one reason i ask...
Thanks for the advice!

Gabby Johnson wrote:

I've always used ethyl alcohol for cleaning. It's a good solvent for the tars in cigarette smoke that a lot of the older typewriters were exposed to, and it dries clean quickly.

Thanks!  I have used it on old gummed-up Leica lens focusing threads before with great results.

Some more robust mechanics dip the entire machine in diesel fuel... or so I am told. I am also told that in the past some repair shops used gasoline, which has to be about the craziest thing I have heard because of the volatility and explosion hazard. Mineral spirits to the best of my knowledge are effectively gasoline with the most volatile stuff missing so would serve the same function. Me, I like to put the machines in a pressure vessel and compress methane to liquefaction for use as a solvent.

Just kidding. Though I bet liquefied methane is a killer solvent. 

Off topic, but I am struck by how even so-called high fuel prices are dirt cheap organic solvent prices. $4/gallon? Get outta town. Earth came with an essentially infinite supply of organic chemicals buried in the ground for our use, which is a very handy thing optional planet feature - essentially infinite that is if we stop squandering the damn stuff by burning it in air as fuel!