well bloody thing started sticking again , master 2-3 years old .
pulled it off , got new spare out of box, thought lets pull this to bits and see???
remove circlip , use 3mm allen key to drift out piston , piston is clean , no corrosion present , seal looks good.
use internal puller to remove nylon sleeve , o'ring underneath held in by sleeve.
slide piston up and down sleeve ...no sticking ?
Hmmmmm.
clean master cylinder housing , internally where sleeve was , slide sleeve in both ways to check for sticking . slide piston up
and down with sleeve in place to check . repeat cleaning til it sticks no more.
put master in vice to hold it.
insert piston , locate in bore , hold piston in bore with screwdriver, drop o'ring over piston , slide sleeve over piston , holding
piston in the bore push sleeve into housing , with your 3rd hand , replace circlip .
check for sticking .
cause is the corrosion between sleeve and housing , just enough to make it stick
you could feel the brake coming on gently as you rode slowly , and then free itself , all without touching the pedal.
pulled it off , got new spare out of box, thought lets pull this to bits and see???
remove circlip , use 3mm allen key to drift out piston , piston is clean , no corrosion present , seal looks good.
use internal puller to remove nylon sleeve , o'ring underneath held in by sleeve.
slide piston up and down sleeve ...no sticking ?
Hmmmmm.
clean master cylinder housing , internally where sleeve was , slide sleeve in both ways to check for sticking . slide piston up
and down with sleeve in place to check . repeat cleaning til it sticks no more.
put master in vice to hold it.
insert piston , locate in bore , hold piston in bore with screwdriver, drop o'ring over piston , slide sleeve over piston , holding
piston in the bore push sleeve into housing , with your 3rd hand , replace circlip .
check for sticking .
cause is the corrosion between sleeve and housing , just enough to make it stick
you could feel the brake coming on gently as you rode slowly , and then free itself , all without touching the pedal.
Couldn't have put it better myself 
