My stem for the knob is plastic, I suppose it may be difficult to maintain a tight fit , not an engineer.
I would not try scotch tape as I have seen what can happen over time, it dries out or becomes gummy and it would be hard to clean.
I have put on the teflon tape as I described at the top of thread and it is a tight fit and has not loosened up. It is such a quick and inexpensive fix and I am happy I havnt been chasing the knob around.
also it is easy to double teflon tape if the gap of your knob is still loose with one piece.