Beeswax and turpentine polish. Homemade?
I wonder if the original formula used artists genuine turpentine. Not the turpentine substitute we get in DIY shops. Two different things altogether.
Artists genuine turpentine can be had in small bottles, Winsor and Newton is a name to look for.
Art shops stock genuine and substitute, so make sure you get the right stuff.
It's only a guess and may not be the answer.
Good Luck, and if you do crack the problem, I might dig out my old Photax Flat Bed out of the loft.