Wouldn’t want to follow you on a motorbike! I think it highly unlikely that such heavy oils would penetrate the leaves, but don’t think it necessary either. Some friction between leaves gives the shockers an easier life.
Exactly my understanding. A charming old boy with a pre-war Aston at Chateau Impney explained to my son & I that leaf springs needed enough lubrication not to bind, but not so much that they lost the stiction between leaves which was an important damping component on bump (but with less stiction on rebound since the leaves had already been displaced - which is exactly what you want - an hysteresis curve to an engineer). His potion of choice was Neatsfoot oil. I had to look it up when I got home. Vegans look away now!
Neatsfoot oil is a yellow oil rendered and purified from the shin bones and feet (but not the hooves) of cattle. "Neat" in the oil's name comes from an Old English word for cattle.
