I just did mine the other day after all this discussion and mine being over due for fresh fluids. Like Noobi said. Any bottle that says "for use in DOT 3 or 4" will cover it. I just purchased from supercheapauto and ended up with Castrol racing which I think is actually a DOT 5.1 spec.
A good 4 or 5.1 is good,, cheap 3 boils too easy if your a brake dragger. I actually use John Deere dot 4 and I do not overheat the fluid anymore. I even overheated some "racing" fluid. Yes I do drag brakes on occasion.