anyone out there know how to tell if a manifold is about to fail. Do all the the manifolds fail on 1998 bonnevilles? If not, why do some fail and others not. Would like to purchase a 1998 bonneville but have heard horror stories about manifold failures causing engine damage, big $$. Should I avoid this brand/model or is there a way to tell if it has already been resolved. Are the replacements the same thing or an improved version?