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Was the rearmost exh manifold stud
broke off on either of these two
cases? Mine was, not sure if it was
a contributing factor, or a symptom.

both my Trooper and Impulse had the same studs snapped. expansion rates of the adjoined metals make it not uncommon for aluminum head motors to bust these studs. an easy preventative measure is to elongate the 4 outer most holes in your manifold/header in order to allow some extra room for movement.

2.6 Trooper
2.0 Impulse Turbo