I was at the store yesterday browsing and I couldn't help but notice that they had six different brands of brake fluid, and only one that was Dot4 spec'd. The Valvoline Synthetic was the only one which stated DOT 3 / DOT 4. Everything else was DOT 3. Even the fancy bottle of Lucas. It seems to me that a few years ago most fluids were 3/4. Is DOT 4 fluid becoming obsolete? Given the option, I don't know why one wouldn't prefer to use 4 over 3 given the higher boiling point.