[davemc]

I lucked out and was able to repair my choke! There was no sign of burning or heat, and no "green disease" near the lead wire connections to the windings, as is often the point of failure. In this case, there was a simple break about 80% into the outer layer of the windings. The only trick was getting it apart without damage. The bottom of the case surrounding the core was riveted to the top, and had to be ground off. The core construction was all separate stacks of E and I laminations, with a thin piece of paper between to form the gap. Then there was a metal wedge retaining the coil to the core. I was able to drive it out without damage using a thin metal ruler.

The gap insulator was damaged during disassembly, so I used a piece of paper removed during disassembly of the choke (probably not exactly the same thickness as the original). I normally use black friction tape when reassembling repaired chokes and transformers.

The winding now measures 2271 ohms - no leakage to ground. Not sure what caused the failure - perhaps just a weak place in the winding, or corrosion. The filter cap in this case was a wet type, which do not tend to short out.