To the left is a damaged knob from a Buick 980868 and to the right is a good knob from another set that I am using for a pattern
I mount the knob on a small plexiglass section. I then dip the knob 5 or 6 times in a latex rubber compound.
I remove the hardened mold and then pour a new knob. I use fiberglass resin. Here's the new knob removed from the mold.
A shaft hole is then drilled, followed by drilling and threading for a set screw. The knob is then sanded and painted. The original knob is to the right