Sticky caliper(s) and/or bad rubber brake hoses can cause brake fluid to boil, and you will lose your brakes until the system cools down. I had this happen on a 450SL, and it was scary trying to slow down from highway speeds for a stoplight. I didn't smell anything funny before, and the car didn't pull to one side or the other before it lost the pedal. The calipers didn't leak either. Degraded brake fluid can boil at much lower temps than fresh fluid also. I rebuilt the calipers the next day and replaced the brake hoses as well. The caliper kits cost around twenty dollars each and the hoses cost around the same. Just my .02 .