over the winter i replace the exhaust manifold gaskets but not the manifold on my 01 2500hd 6.0 vortec.. they were fine until recently started leaking again . i checked all the bolts and they are tight .. is it possible the manifolds are warped or something ? Im willing to install new gaskets and manifolds is there a good brand of gaskets that might eliminate that annoying exhaust leak? or is there a trick to getting them to seal perfectly ? please help this is driving me insane ..