Do yourself a big favor and buy some brass exhaust nuts. Alloy expands twice as much as steel which makes keeping steel nuts almost impossible to keep tight. I suspect the crack in your head was caused by the alloy not being able to shrink fully on the steel nut (possible)???
I bought chrome plated brass nuts and they loosened up like the iron ones do....think I got the brass ones from NORVIL. The brass nuts stay put so you can toss all the tab washers wire and springs. Brass expands at the same rate aluminum does.