Front brakes.

[His Dudeness]

The calipers I've done the problem has always been from a chewed up dust seal or corrosion and dirt behind the dust seal pushing it out of it's groove. Either way the dust seal was stopping the piston moving freely and needed to be replaced. I'd recommend Yamaha seals the after market ones are a bit hit and miss in my opinion whereas you know the Yamaha ones will fit and be good quality