X4 on the Glyptol.
The power plant I worked at used Glyptol on EVERY motor, both exposed armature windings and the field coils. They claimed it prevented "working" of the wires under magnetic stress, and consequent wear-through of the varnish insulation.
It is a bitch to get off for re-winding, however. By the time you get to that point you're talking a major rebuild anyway.
It is also used a lot on the interior of cast iron motors/transmissions after tanking or blasting. Seals in the errant pieces of sand or grit and makes an interior surface the oil can "slip down on" easily.
https://www.amazon.com/Glyptal-Brush...516BM8VVKG3WC7
Joe K