When you say "synthetic" brake fluid I believe you are referring to "silicone" brake fluid. There has been alot of information about this topic on this site, so I would try your search using "silicone".
I think that most people use regular brake fluid (DOT 3) due to their familiarity with the product and it is true there are compatibility issues with rubber cups in the master and brake cylinders. Still, there are some who advocate silicone (DOT 5).
Kent
