Silicone Brake Fluid
It's DOT 5 brake fluid. Newer Harley's are useing it so it is becoming a little more common. You should be able to get it at any larger auto parts chain, if not Advanceautoparts.com (Partsamerica.com) should have it. It's not cheap. Make sure you don't have any of your old fluid left in the system. When I do my final one over on my '68's brakew system I'll be switching over... I'll be changing everything so I know I wont have anything left in my system (master, prop. valve, lines, hoses, wheel cyclenders, calipers). If I'm going through that much trouble I'm going with the stainless lines and putting the best fluid in it.