[sick472]

I had a similar issue with an old switch installed in the dash and could not get the new replacement knob/shaft assembly to stay seated. It might stay firmly in the switch for a pull or two then it would just pull out with normal force. I noticed that the new shaft end that goes into the switch was barely different than the old one. I had to take it to the bench grinder and remove just a hair off the end. I don't remember the exact details as to what I had to grind, but it went in and has not come out since. I want to say that the very tip was just a small bit too long and not allowing the shaft to go in far enough for the catch to pop into place. If your knob does pullout, compare it to the other knob shaft and see if they differ.

Just 2¢ for you or someone else with the same problem. I really don't see how the plastic knob not being on the shaft could make a difference, but anyhow, glad your good.