Rebuild service for combination/proportioning valve

[Accelo]

In my limited research I failed to find the law that addressed this;
Illegal for a business to rebuild or tamper with in the State of California.
If anyone can find a link to the statutes it would be appreciated.

I did find information on how to rebuild the 1978 - 1982 GM 1257208 Combination Valve Rebuild;
https://www.musclecarresearch.com/gm-1257208-rebuild

And the rebuilding kit here;
https://www.musclecarresearch.com/gm-pd-valve-kit-3