Yes, DOT 5 silicone is hydrofobic. I was well aware of the controversy concerning silicone brake fluid, but I decided to take the plunge after the recommnedation of a friend of mine. He has an old Mercedes, an even older Nash, an MG TD, a Volvo PV and a +8, all changed to silicone, but no changes to the braking system. No issues at all. Of course it was done a VERY thorough job when flushing the old DOT 4 out and then changing to DOT 5, as it was done on my car (with his help). Besides, all the military vehicles in the Norwegian army use silicone, just because they are stored without use for extended periods of time. If I am not mistaken this is as a matter of fact a NATO standard. Correct me if I am wrong.
It is said that if DOT 4 and DOT 5 form a gel when mixed, but it does not seem to be true. We simply tried it in a glass. No gel, they just don't mix - like oil and water. And it is said that DOT 5 makes rubber parts like hoses and gaskets swell. If this is true or not, to what degree or if it has any practical importance I do not know, but as I said I have not heard of any issues.
