Exhaust manifold heat expansion and contraction causes the brittle factory exhaust studs to break. Like many owners, the bolt at the back of the engine on my Silverado sheared flush with the head and would have been a massive pain to extract. The problem is so common that Dorman makes a bolt-on corner clamp to hold that position on the manifold in place.

Exhaust leaks will cause the computer to set a misfire code and illuminate the check engine light. The CEL prevents the torque converter from locking at a steady speed, which lowers revs by several hundred RPMs and helps noise and fuel economy.