So my big thought with the DOT 5 is that it doesn't eat paint the way DOT 3 will. I have yet to have a master cylinder that doesn't wind up with some amount of seepage from the cap running down the front of the brake booster and dripping onto the frame. With all the hours I spent on my engine bay, this little fact got my attention. Apparently, the older seals are not the biggest issue, but is seems that it is a big problem for ABS systems. Just found a good comparison article here: http://www.superchevy.com/technical/chassis/brakes/0509sc_fluid/index.html and another interesting bit from another article. "The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas." The bottom line sounds like although it has a higher boiling point (and doesn't eat paint) the drawbacks that go with it don't make it worthwhile.
Brake fluid Now that is very informative, I had thought that the largest users of "silicone" were Plastic Surgeons in Beverly Hills. lol TJ