I've been running Dot 5 Silicone brake fluid in my 37 pickup since the early 80's (when is was cheap to buy) without any problem. I recently installed a new rear end in the truck, a dual master cylinder and replaced some older brake lines, like the originals, and am a very Happy Camper. No trouble what so ever.
So, I recommend Dot 5, and if you think you will get stuck on the road needing some, they have loads of the stuff at any Harley house.
