Simple PE Knob Repair Question

[strikers1945]

I have a PEK which I have PE-upgraded with the Prophet-style knobs. I am sure I am not the first person to [tweak/love] the Low Pass Frequency knob until the knob's indicator cap came off. I am looking for a recommendation for an adhesive. I'm not sure chemically what the knob core is made of (what grade plastic). Are people just using superglue? I certainly don't want to use anything that would eat the plastic. Sorry if this has been answered elsewhere, I didn't find the info in my moderate searching. See Attachment.

[Sacred Synthesis]

Some of the Prophet style knobs have a tiny metal ring that fits inside the hole in the knob.  If the ring falls out, the knob no longer fits snugly on the shaft and will fall off.  You ought to look to see if this is the case with your PEK before you try applying glue.  If it is, you might be able to get a few spare knobs from Sequential, or possibly on Ebay.