OT : old US Telephone hybrid ('Network' block)

THis is off-topic, I know, but I suspect there are some people here interested in old telephones. I have a Western Electric 500 telehpne on the bench. The standard US rotary dial one. As you may know, all the small components and the anti-sidetone transformer ('induction coil') are in the metal box kown as the 'Network'. This is the normal type 425 unit Anyway, I've remvoed this from the rest of the 'phone by disconencting the wiring and drillign out the rivets (this was standard practice accordign to one of the official repair manuals I read). I can refit it using 6-2 UNC screws whcih are a perfect fit. The 425 network was not field rpeairiable, and I can see why. After bending up the tabs, I slid off the can to reveal the components in a particularlly evil potting compound. It's not hard, it's sticky, I can be scraped off (but I spent good quarter of an hour clenaing a screwdriver after this). It will soften with heat (in fact a hot air paint stripper gun wil lget it to drip off, but I was gettign the thing so hot that the plastic terminal board was softening too). No solvent I have tried will remove it. The BSP docuemtns simply call it an 'insulating medium' which is not much help :-). Has anyone ever repaired such a Network block and knows how to shift this stuff? -tony