John,
You did not say what model coach you have. However on most of the Hurricane heater exhaust systems on Beaver coaches the point that fails is the elbow located just below the heater. This elbow is not a standard exhaust part, but it is actually a copper plumbing elbow that you will have to purchase at a large plumping supply store, because most small plumbing supply stores do not carry copper elbows above 1 1/2 inches.
Gerald