Quoted from vireland:
I feel that a metal heat sink on a coil with coated metal windings is an accident waiting to happen. I would never risk it.
I can respect that. But for what it's worth, those same coils are already mounted to metal brackets and moving parts, and even used metal sleeves until the discovery that nylon sleeves have less friction against a metal plunger, so done properly a sink could be just as safe. Maybe the coil could be wrapped by thermally conductive - but electrically insulative - mica film and have the sink clamped to that.
Just spitballing alternatives... I (and the rest of us I'm sure) appreciate your research and efforts into solving these issues.
I've experienced thermal coil depression on some of my (older) WMS games during long parties and expos and such so I do agree it's a legit phenomenon, but those games usually aren't quite as sensitive to it, shot wise... so while I never felt compelled to consider it a big issue, may I could experiment after all. Of course now that I'm thinking about it, if the coil expands too much while hot, a clamped sink might not be a great idea anyway, lest the coil then be forced to expand inward against the sleeve/plunger. D'oh!