Ever try fixing cordwood construction units, especially those lovely ones that were potted to keep the arcing down.
There the ultrasonic cleaner with the tricholrethylene and the vapour phase cleaning section worked a treat. It would get the epoxy soft after a 30 second immersion so you could pick it off, then as a final step a 3 second dip and a 30 second dwell in the cold zone to get the vapour off and you could then fix the unit, then pot it again. You could buy new, but as they were made from Unobtanium you had a lead time issue. Regular 30kV diodes, high voltage resistors and capacitors were easier to get hold of.