Removing stuck shift lever knob

[wrndln]

I have a shift lever assembly that has a decent original knob on it. However, I can't remove it from the shaft. It is hard to get a good grip on the knob to try to turn it. I hate to heat the shaft as it might mess up the knob. Penetrating oil hasn't worked for me well on loosening parts in the past as well as heat does, but maybe if I soak it for a few weeks in penetrating oil, it might work. I don't think penetrating oil would damage the black knob, but I am not sure. Does anyone have a good way to get it off?
Rusty Nelson