Agree with JJH fear mongering bollox.
My experience, when i first got my GSA the local dealer recommended my bike needed a service also stated that the fluid needed to be changing as it hadn't been done in 2 years. So i had them change it. since then i have serviced the bike myself.
2 years later i flush the fluid expecting it to come out discoloured and also expecting a difference more sharper braking the fluid that came out was the same as the new going in and no change to the braking performance.
I decided to give it a four year gap which was done about a year ago when i last serviced my bike. the fluid that came out was only slightly discoloured.
Again didn't notice any difference to braking.
My bike is garaged, every year i do trips to the Pyrenees and Alps where the brakes get heavily tested, i have never felt any brake fade I have done 40K on the bike since 2011
I wont change my fluid for another three years.