I copied the Diosol formula posted in one of the yahoo groups several years ago by a chemist who lab analyzed and posted the formula. This is as posted verbatim.
"38% by vol toluene, 41% by vol xylene and 21% by vol Solvesso 100 (a long evaporation rate aromatic hydrocarbon solvent). Getting the toluene and xylene is not difficult, but the Solvesso 100 is only available through chemical suppliers."
I was fortunate to have a local paint manufacturer that could provide the Solvesso 100.
Also, I would never soak anything other than metal in Diosol.
BTW, I'm looking for original formula Floquil RR10 Engine Black, the exact number must be RR10. Bottle, box, can, case......