I think I need to post a photo to clarify. Yes the knob has a non-separable off-white inner plastic part. There's another separate small white plastic collar in which the female spade terminals sit once everything is together. The problem is that collar doesn't fit up through the bottom of the knob but the spade terminals can't slide down through the collar to allow it to be installed down from the top of the knob. I was only able to get the old knob off because its integral inner collar was broken (which is why I had to replace it in the first place).

It sounds like others who have done this have not come across this white collar (the separate one, not the one that's part of the knob).

Zack
1980 245DL M46 290k
1988 745T+ M46 233k
1989 245DL M47 149k