I had Musky's problem years ago on a Yamaha XS 650. Front brake working fine, then started to bind more after each use. Realised what was happening, so saved the disc. Roadside fix was to slack off the feed pipe, sacrifice a few dribbles of fluid and pull the caliper against the disc to retract the caliper piston. Re tighten the feed, ride carefully and avoid using that bad brake unless you have to.
Simple cause, in this case alloy crap blocking a fluid return hole in master cylinder, so master piston staying in the "on" position. Bet Musky's is similar, even a manufacturing fault, or a coincidental failure of a rubber hose playing the one way valve trick.
Swarfy.
PS. Nice one Bergs, Fine Dining in Buxton. Ferodo Factory not far away.....just out of interest.