Any track will have some sort of stewarding set up; ask tech and they will tell you exactly what you need, what you can do, and what you can't. In fact, the more organized and by-the-book those guys are, the more comfortable you should feel using that track.
The radiator top seam tends to fail where it meets the metal. Also, in rarer cases, the top hose leaks where the clamp holds it onto the rad, and sometimes this only happens when the system is pressurized and the top hose is moving (as in, when the motor pitches as the car is driven). It is most likely the rad itself though, at the top seam.