My first thought was overheating as well. And what you say is not true. Boiling does not "put" air into the system. It causes the brake fluid to vaporize and turn into a gas. When it cools down, it becomes liquid again. After it has boiled, the brake fluid loses a ton of its efficiency. Thus if the fluid EVER boils, you need to flush immediately because it's no longer good.

As for floating pins... I'm not sure about Bendix calipers, but Girling calipers have floating pins. The calipers are attached to the caliper mounting bracket through the use of floating pins. These are sometimes called caliper guide pins, or sliding pins. There are tons of names for it. The bottom line though is that these pins need to freely move in and out of the caliper mounting bracket. If they are seized, your braking will show abnormal signs such as not disengaging or sometimes not engaging at all. Obviously if it did not disengage, the brakes would heat up a LOT leading to premature wear on your pads as well as rotors.
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Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'