We had my zr 580 brakes stick my buddies polaris triple, and my buddies ski doo 670 mxz. Bleed out all of the fluid its probably old and gunked up and the pressure from the pad end isnt going back up into the float once u release the brake.
Best thing ive found was to pump some air through it after you have most the fluid out. Each time it was the same thing, gunk stopping fluid from returning which causes pads to stick. The 670 actually lit on fire a couple times till we made it home lol. brake rotor was red as a cherry.
blowing air through the line is the important part, you've gotta get that gunk out. after that new fluid bleed again and cap it off once u've go the air out should run like a new brake system after that.