Your post made me want to dig into this a little more (plus I clearly have nothing better to do with my time
) and you're dead on.
Hoppe's #9 formulation has changed quite a bit even between 2016 and 2019 and not just re: Nitro. They took out a major component used as a SS protectant (oleic acid) sometime between 2016 and 2019. Not clear on what they replaced it with.
2016 (still had
9 total ingredients) in order of %: acetone (polar), ethanol (slightly polar), kerosene (nonpolar), oleic acid (nonpolar, protectant/emulsifier), propane (nonpolar), N-butane (nonpolar), N-Amyl Acetate (nonpolar, banana smell), isobutane (nonpolar), and citronellal (polar, lemon smell)
2019 (now has
16 total ingredients), in order of %: Kerosene (nonpolar), ethanol (slightly polar, used as emulsifier), propan-2-ol (isopropyl alcohol) (highly polar), amyl acetate (nonpolar), 2-methylbutyl acetate (polar), methyl alcohol (slightly polar, used as emulsifier), <1% of ammonium hydroxide, <1% various other things.
I like the look of the 2016 formulation way better than the 2019 b/c in the 2019 version I'm not sure off hand what they are using as a protectant (the 2016 version uses oleic acid for this).