Due to no fault of my own, an eletric motor's copper coil windings took a bath in hydrocarbon oil, which left a sludge.  What is the best way to clean the coil windings? IPA?

if this doesn´t work try diethylether (starter spray). But will work. Works much better if slightly warmed up before use (~35°C - 40°C). The copper coils are coated(insulated) anyways so you won´t have to worry to much, just be careful with acetone (ketone) or chlorinated solvents (tetrachlorethylene etc.)