The contacts for the starter button inside the switch very often gather rust and corrosion over the years and make a poor connection, so the problem maybe as simple as that.
Its just a case of removing the switch from the bike and sit with it over a large sheet of white paper to see if anything drops out when you take it apart.
Take photos at each stage and give all connections a good clean and thin coat of grease where appropriate.
Should be ok for years after that.
Pete F
UK (or whats left of it).
Why Have Four When You Can Have Six ?
