Originally Posted by
dabac
Baby oil is primarily White oil/Paraffin oil. A very harmless substance.
Anything OK to smear on baby skin, and is given by the pint to constipated horses is hugely unlikely to upset polymers and plastics.
I’d be wary about performance variation over temperature though.
To continue your digression, I've never seen a vet administer Johnson's Baby Oil and I probably never will as the perfume in it has only been tested topically, according to the FDA. See "For external use only" on the label.
Not sure how the safety of a baby's bottom will translate to a hydraulic brake, but maybe it will give the OP some comfort. Guessing about it's effects on a bike brake system could be exciting. How hygroscopic is the perfume? What is its vapor pressure and viscosity versus temperature? Does Johnson's Baby Oil's viscosity index match that Shimano's specification?