Had some of the rock epoxy, so dropped the whole lot into a bottle of MEK, and left it there for 3 months, till the epoxy was soft enough to pick off. The little PCB in the middle did not survive, but at least I was able to see what it was, which was a simple JFET buffer module for some chart recorder, of which I only had the buffer. Resistors all I had to measure as they also lost the paint. The capacitors, metal film, were dissolved.