Time to rebuild?

Good you determined it is an O/F problem and the engine is sound.

That has not yet been determined. There's still blowby to deal with, and this car's constant short-trip usage with the choke far too rich (no pull-off action) means there's still a fairly strong likelihood that a rebuild will be required.

I don't know if most mechanics then even understood how it was supposed to work.

The good ones did.