Front brake effort fluctuation

[Otley77]

Hi all, here's the thing: my R1200RS has slight fluctuation of brake effort, its an advisory on the mot. Braking is fine, I can feel slight fluctuation, more noticeable when coming to a full stop, for the last few rotations of the wheel.
It's not a serious problem, annoying and spoils the ride a little.
Any thoughts on a straightforward and not expensive fix?