| basically excluding the dot5 silicone stuff, the higher the dot rating the higher the boiling point and the higher the performance. the trade off is the higher the boiling point the more hygroscopic the fluid is, that is, the higher the dot rating the rate of moisture absorption INCREASES.
dot 5 silicone based fluid is a good choice if you are paranoid about paintwork(as i am!)also, it does not absorb moisture, rather, any moisture that contaminates the system will gather seperately and when the system is used the water boils and turns to steam. this gives a very spongy feel and if you don't bleed them regularly (much more than glycol fluids) the water builds up and can cause serious corrosion and your brakes may fail. also, brembo seals don't like silicone fluid much (apparently) but i have had no problems.
if you are contemplating changing you should change all seals, though this is easier said than done, considering how parts are VERY hard to get. at a bare minimum you should drain the glycol fluid completely, refil with meths or similar white spirit, flush repeat, leave open overnight to dry. fill with silicone fluid, flush and refill and bleed.
remember to change often.  | 
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