OMC Manifold End Cap Gasket | Sierra 18-2861-1 Gasket for front end cap of OMC inline 4 & 6 cylinder exhaust manifolds from 1971 to 1990. Sierra exhaust end cap gasket For various OMC 100, 120, 140, 165, 2.5L, & 3.0L stern drive marine engines from 1971-1990 Replaces OMC 311121 Replaces Sierra 18-2861