I remember back the first time I used silicone fluid about attacking rubber, I asked and was told only old rubber combinations, not newer. This is a quote from a website ( In addition, silicone fluid is affected by atmospheric pressure. When a silicone brake fluid-equipped vehicle is driven in high altitude conditions, the fluid can expand significantly — again contributing to a spongy pedal. Further to this, many of the rubber components used in brake systems are manufactured from “ethylene propylene rubber”. Some silicone fluids are not compatible with the “EPR” – causing them to expand)
I have and still use both DOT 3 and DOT 5. As stated silicone has some problems as far as leaks, spongy pedal, but for the most part I think we are good as far as the rubber that it attacks.
Steve