Get a real strong flashlight/torch and look follow how the rear brake line runs from the master cylinder. It doesn't go anywhere near the exhaust. If any spot is getting hot there is a section in front of the engine. Yes, it runs forward all the way to the front of the engine, then goes from braided to solid line up and under the tank to the abs modulator. All the air collects there, no where else for it to go. Until you vacuum it out. Just regular bleeding gets some of it, but the modulator has to be pulsed while bleeding to get that air trapped in it. Just riding and braking hard doesn't remove it or let it get back to the master cylinder. It just releases some fluid to lower the pressure. The air is still there. When mine was done by the new procedure the whole bike was shuddering and puking out big shots of air. If that solid piece of brake line is getting hot it must be from the engine block after the braided section goes across the front.