The source of this info is the Cadillac-LaSalle Forum, and CLC Member Geoff Newcombe

Geoff Newcombe CLC #4719 -

Cadillac put their exhaust manifolds on for many years (do not know when it started) without exhaust gaskets.  I have always been told (and have always done so) that when you have to take the exhaust manifolds off, always use gaskets when reassembling.  They should be readily available at your parts store, and are part of any overhaul gasket kit I have seen.