1. Remove the brake line from the MC and the rear brake fluid reservoir, brake fluid is corrosive so cleanup any that is spilled. Then using a set of internal circlip pliers remove the circlip:
2. You can then pull out the tube and its o-ring - this o-ring doesnt come in any of the rebuild kits ive seen:
3. You now need to unscrew the locknut and then remove the clevis, this is what you use to set the position of the brake lever:
You then remove the rubber boot - its just a push fit, if its covered in debris you can grab the top of it and "twist" it to break the seal...it will come out to reveal...
4. A circlip (notice all the crap thats gathered in there after 24 years without a service), this holds back a plunger and a metal washer, this can be difficult to remove depending on the level of encrustation down the barrel, if yours is beyond hope new plungers can be ordered from cradleys for ~£30:
5. This is what you will be left with, give everything a good clean/wash/sonnication, buy a new seal kit and replace the "worm-drive" piston along with its seals and spring, and the rubber boot...assembly is the reverse of this procedure.
