Yes, the one piece manifolds, whether on Caterpillar or Cummins are susceptible to manifold cracking and/or gasket leaking. Not a high failure rate item, but it can happen. If just warped they can easily be resurfaced-- should cost around $25.
There is a current thread on another forum where a number of Cummins C engines exhaust manifolds shrunk-- identifiable by bending of the forward most and rear most bolts. Replacement is the only solution if this happens.
Some engines have an upgraded three piece exhaust manifold that significantly improves exhaust manifold life.
BTW, same thing on larger gas engines-- 460 is a poster child for exhaust manifold problems.
