Swanny, it won't just "expire" after 6 months, but it absorbs so much water it drops the boiling point down below a safe level. Like any brake fluid (which generally lasts only 2-3 years at the most) you'll never notice when it goes bad on the street because the fact of the matter is most of us don't drive that hard on the streets and don't push the brakes that hard. But, if you needed to, with the old fluid, the brakes might not be there for you when you most need them. This is why most tracks (I'm not talking drag racing) require brake fluid to be fresh, and at the most, only 6 months old and not discolored at all to be considered safe.
Here is a quick link for you with some basic brake info. Its on EvoM, but it pretty much repeats all the same stuff discussed on auto-x, S2k, etc. forums:
http://forums.evolutionm.net/evo-tir...ct-thread.html
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