SEAL PISTON

Sometimes, bleeding your brake system with a new piston seal fitted may be all that is required to restore the brakes back to normal. If you are already committed to fitting a new piston, then the seal has to be replaced as a matter of course.
For all the likely parts you may need for a thorough brake overhaul for your classic Honda, try browsing the online 'parts list' fiche, where applicable, or the catalogue for your type of machine?