AO Platinum Member
Join Date: Feb 2002
Location: The land that Time forgot
Re: Brake Fluid
Aye! DOT4 is DOT4,
DOT5.1 is a better version of DOT4.
DOT5 (cf DOT5.1) is the synthetic one that does not absord moisture (but also does not lubricate the seals, which some systems actually need) and any water that does get in, is not absorbed, so collects in one place and rusts your brake like from the inside. Only good for frequent-change applications, like motorsport.
DOT4 changed every year is better than DOT5.1 changed never.