This is a brief insipid observation with a conclusion. I've seen another electric motor where replacement wiring was the wrong type and caused problems. The original is a certain gage with a rubber type inner sleeve. It is surrounded by a woven shield and often that was shellaced or otherwise treated. The surface treatment was to insure its integrity where it was and these arrangements lasted decades. They are brittle and crack, when moved, from motors which ran for years of time and then the replacement wiring is wrong. What "was" the best thing has shown to be less durable. Newer, "rubbery" wire insulation failed and became a carbon track to shorting out grand old fields and such.
There is exact type wiring for their environment and that is the one to use.
It must occur to me that changes happen over time and ancient wiring is something to inspect at times. If a circuit has been used for 70 years or more, changes can take place in the insulation. Can't say but a heat detector might be a good thing to aim at every switch and outlet. If a loose connection over time has further degraded (by higher voltage) the insulation by heat, there is a thin edge of woven over possible carbon.
So. While they are cheap, a point heat detector makes sense. It could aim you at a line which needs to be tightened or replaced.
This is more associated with BX which have their own case, yet they exit. Even if they don't, over time a wire may have been yanked or just plain old, admitting a current and heat situation.
Just saying it would be good to see heat readings on the various lines and watch for the relative differences.