[Arran]

Mike;
I've only run into a speaker with an open filed coil twice, and they were on newer speakers from the 1940s. One was in an Addison radio where some dummy drove a screw into the coil, or ran a drill into it followed by the screw, so it likely had two dozen or more breaks in multiple turns, the other was in a Serenader radio, made by Electrohome, where the output filter cap had shorted burning the thing out. All of my other inductor problems in the audio output stage were open primaries on output transformers, or on audio interstage transformers, the latter seem to fail almost as often as filter caps.
I noticed something interesting, the top end of the pole piece has a pair of holes machined into it like they used a spanner on some sort to hold it whilst they cinched down the nut at the other end. I'm not sure hole large the holes are but I think a spanner from an angle grinder might fit, the type made out of thick wire, and that are sort of springy.
Regards
Arran