[Mark IV]

Perhaps Jay will chime in and confirm, but I seriously doubt it is silicone fluid. I would use DOT 4 and be done with it.

I don't know of ANY manufacturer that factory fills silicone fluid. The benefits of silicone (non-hydroscopic) make it a liability for a daily driver, i.e. any moisture (and there WILL be moisture) in the system will pool at the lowest point of the system and cause corrosion at that point. Glycol fluid will keep the moisture in suspension so it can be removed when the fluid is serviced at a fluid change....you DO change your fluid semi-annulally, right?