M.B.Changed the components and design on the OVP and FPR a few times during the lifetime of use.

These components are now up to and above 20 years old and more.

The components can change their electrical characteristics over that time especially being subject to extremes of heat or cold as the whole vehicle is subjected to.

Finding new individual electronic components e.g. Zener diodes that were in production 20 years ago is not the easist of tasks - especially when they were produced in third world countries in a limited run basis.