Rust is still a problem with those little ferrite rings, though. Depending on the environment you maintain for this device, it can actually be pretty delicate.

Rust is still a problem with those little ferrite rings, though. Depending on the environment you maintain for this device, it can actually be pretty delicate. I have some old (~25 year-old) electric motors, where the magnetic properties of the bigger ferrite rings have been degraded by rust. I guess it probably depends of the quality of the piece. This means there could be one tiny rusty ring in one of the center planes, and that would effectively result in a bad block that exhibits inconsistent behavior for that single bit. A person would have to test for that. It could be programmed around, and you could still have a fully functional object, minus one byte or word (or bit, depending on how you approach it). You'd also want to keep it free of dust, since dust CAN be metallic, magnetic and conductive. The item for sale looks like it's been taken care of nicely!