I've personally had rust develop on the foils of a Braun series 3 shaver head from trying to save a buck and clean it with a non-braun solution. Fortunately one run through the clean and renew station with proper Braun solution took it away.I don’t dispute your comment because in the five years that I shaved with my Panasonic ES8103 shaver I rinsed it under running water and never applied any type of lubricant nor did the owner’s manual mention lubricant. However, here is the quote from the Braun 7 series owner’s manual. “
If you regularly clean the shaver under water, then once a week apply a drop of light
machine oil (not included) on top of the Foil & Cutter cassette and the long hair trimmer.”
I assume mineral oil would also work. I assume that the Panasonic screens and cutters were stainless steel which wouldn’t rust. Maybe there are parts in the Braun screen/cutter cassette that will rust if not coated with oil after washing the shaver with water.