[ACademic]

I would focus on a small section of the car and start with chemicals that are the least caustic. Plain lacquer thinner can be used safely on bare aluminum and should be strong enough of a solvent to break down the silicone. WD-40 is also known for its silicone-eating properties, albiet it's a bit more oily and may need to be followed-up with a swipe of the lacquer thinner. You could also research materials that body shops use to prep a car prior to painting. These all have silcone-removing agents that are safe on primers and fillers, so it should also be safe on bare alloys.