Removing old potting material from a transformer --

I have a 10-volt transformer, built by Jefferson Electric circa 1926,
that goes with a Welte Philhamonic pipe organ roll changer, and several
of the leads were broken off where they entered the transformer housing
through little porcelain insulators.

There was no way to repair the leads so I removed the transformer which
was encased in a reddish-brown potting material.  The input and output
leads were also encased in the potting material.  I've chipped most of
the potting off the transformer and I think if I can clean the rest off
I can renew both sets of leads and salvage the transformer.

I have no idea what this material is, but is there something that will
dissolve it without damaging the windings of the transformer?

If I can accomplish this and put on new leads, does the transformer
have to be potted again inside the box or could it be mounted inside
with silicone rubber?

Thanks,
Dave Krall