I picked up on Aero Kroil back in the 70's. I had a friend that worked in a shop that did big buck restorations on vintage cars. Some of their restorations had sat for 30, 40 years before they were taken apart. Their choice for loosening nuts and bolts on these vintage cars was Aero Kroil!!!! If it is good enough for use on a priceless Talbot-Lago or a Duesenberg, it is good enough for use on my Kawasaki's!!!
1972 H2 750 Cafe Racer built in 1974.
1976 KH400 Production Road Racer.
1979 Kz1000 MK. II Old AMA/WERA Superbike.
1986 RG500G 2 stroke terror.
1986 GSXR750RG The one with the clutch that rattles!
This guy actually did a pretty good comparison trying to use the same set of variables on 6 different popular caned "penetrating" oils. All while recording his results and using a spread sheet to graph them all out. His findings show Liquid wrench as the top performer and also is the most cost effective.
That said, I normally don't have the luxury of letting anything soak for days, let alone hours when I am working. What >I< look for is something convenient (and cost effective) that will lubricate the fasteners once I break them loose, more than any "penetrating" characteristics. (Also that will not spill all over my truck / tools, that I can toss around) And to prevent metal on metal galling on certain pieces of equipment.
BUT, normally when I drag a dead bike home, I do try to soak the entire thing in some sort of spray on "penetrant" depending on what I have handy at the time.
1981 Kawasaki Kz1000K1
Located in the Saint Louis, Missouri Area.