Concentrated nitric acid.*
*Warning: may dissolve the copper winding, and iron core, faster than doing anything at all to the potting. Also, rather nasty. Don't actually do this.
Resins can usually be swelled with a nasty solvent, like methylene chloride, but that disrupts or swells or dissolves a whole lot of kinds of plastics and resins and such. So you might end up with clean wire... too clean.
It does matter if it's actually silicone, or epoxy, or urethane, or polyester, or... any of a number of other possible resins. They've all got their flexible varieties, so it could be kind of anything just based on appearance.
Why do you need to "rescue" it out of there? It looks quite happy where it is, and has a free heatsink besides!
Tim