nickleinonen you have the DOT 5 backwards it does NOT absorb water (it is silicone based as opposed to gycol in 3/4) and the water that does form in brake system "puddles" in the brake system resulting in a portion of system being water with boiling point of 212 (not really but essentially) which can cause localized freezing and boiling. More info is in the new TDR(issue 43) page 16. It should not be used in DOT3/4 brake system.
Okay looking over the brands we have raced with or looked at purely the manf specs and our finding of wet brake fluid needing changing or brakes had become spongy (not very scientific as some tracks are harder braking then others and humidty varied as well)
Brand/ price/ dry boiling point/ Wet boiling point/ time between changes
Castrol GTLMA $ 446 311 every 4 hours (we overheated this BAD)
Valvoline Synpower$$ 502 343 every 20 hours
Motul600 $$$ 593 420 every 6 hours
Motul5. 1 $$$$ unk 365 never tried
SilkoleneProrace2000$$$$ 572 383 never tried but I intend to try this next year.
Ferodo5. 1 $$$ 500 unk never tried
Price key per quart/liter $=<5 $$=<10 $$$=<20 $$$$=>30
Here are some of the websites for ref.
http://silkolenestore.com/prod_detail.asp?ProductID=287 http://www.motul.com/uk/produits/index.html http://www.ferodo.co.uk/ferodo_home/
http://www.valvoline.com/pages/products/product_detail.asp?product=51
I will restate this the BF with higher boiling points have without exception required changing more often (twice as often normal)and cost a lot more.
Oh this should be repeated do NOT use DOT5 the seals are different and
can cause issues; drying out of seals thus leaks.