Try boiling in vinegar, but make sure your fan/hood is on, it's super potent (if you can boil it outside, all the better). Okay to dilute the vinegar first, and slowly increase the concentration until it works.
Both citric acid and vinegar have worked best for me while boiling.
If there's lube and gunk left over even after subjecting it to citric acid/vinegar/stp, you might have to go stronger with I think mineral spirits or something. I ended up sandblastic the pf holder since I couldn't get years of coffe n lube gunk out. Wish I had taken a pic after boiling in vinegar, citric acid, and attempts with the dremel but before the blasting.
Before:
After: