Use the correct size Allen wrench and back out the set screw until it's flush with the outside of the knob. Then mix up some JB Weld and carefully drizzle a bit of the stuff into the gaps between inner boss and skirt. You won't fill the voids all at once so expect to make multiple passes. Clean up any overruns or spills as you go - use the toothpick or a Q-tip. Don't allow the JB Weld to begin to harden on places where you don't want it to be.

JB Weld is very viscous and even though the hardening reaction is exothermic - resulting in slightly easier flow - the mixed compound needs a little help in penetrating the nooks and crannies of the knob. So...support the bars by grasping them firmly between thumb and forefinger of one hand - boss side facing up - and using the forefinger of your other hand to repeatedly tap the knob face/insert area. You can also tap the knob on a tabletop or other non marring surface...whatever works. The idea is to simulate the actions of a concrete setting tool without actually putting anything in the JB Weld. That gets messy.

IMAG0563.jpg

Here, you can see the partially finished work. I added more JB Weld after taking this picture, slowly building the level up to "flush" with the outer skirt.