My Japanese spec VX brake fluid needs topping up, I have tried to obtain DOT3 as it states on the cap but so far no luck. Having read on the cans of DOT 4.1 and 5 that it exceeds the spec of DOT3 I am a little wary as the existing DOT3 may be synthetic and the DOT 4.1 or 5 may be a different base material can anyone shed any light on this subject?