Col in my experience even changing the seals doesn't help.
if you ride the bike hard it seems to cook the fluid, most likely because the master cylinder gets heat transfered from the crank cases. My 996 and 998 did this and my st4s does this too.
My solution has been to fit a 'braking' wavy rear disc, which works much better. I've also changed the fluid to a synthetic 5.1 high temp racing fluid. It still goes away if I stand on it a lot (e.g. 5 days in the alps), but generally works great, and it does come back again once the fluid cools a bit.
I think it is called brembo LCF600.
My local bike shop use Motul fluids, and that is what they put in for me at the last service.
The daddy of all racing fluids is made by castrol, but its 4 times the price of the others. You can't mix it with anything else though.
Hope that helps.