mechohaulic

that cross bar isn't made to take  excessive torque . if it keeps breaking/ snapping I would check the vehicle for problems else where == broken crossmember ,brace. bracket , loose bolts etc. it's official name couldn't tell you.  just a lower support bar, old B's/ R's had cross bar used to hold cross over fuel line and lite support even they broke /cracked. we all know no longer lower fuel cross over. 

a good set of left=hand drill bits many times make the job easier. have seen people use right hand drill bit on broken stud which wasn't that tight. drilling to use easy-out will tighten broken stud. left-hand on occasion helps loosen. your situation, i'd let it go unless exhaust leak starts.  extended exhaust leaking will act like plasma cutter and will channel a grove in manifold. drill center of broken stud / spray penetrating oil and run it engine heat with penetrating oil might help the cause.

hopefully the forum will receive an update . any doubt run the one fitting the driveshaft. 

the shutters operated based on engine temp. never noticed but the fire trucks MAY HAVE  eliminated the shutters to maintain cooler eng temps. for the most a fire truck spends engine time stationary ;goes up down the  road but at a fire it's sits. there are a number of VERY knowledgeable fire truck personal on this site. many of which will prove my thoughts incorrect.