The original insulators were a phenolic resin impregnated cloth matrix. My guess is that the cloth fibers seem to get saturated over many decades and lose some of the resin. This leaves it slightly porous and the fuel is absorbed and wicks thru to the outside of the Bakelite insulator. The new insulators use powdered filler rather than a fabric matrix so they are not subject to this however they are also not very good in compression and are more prone to cracking.
Denny Graham
Sandwich, IL
