Mercedes 280ce, w123, exhaust manifold, emission, pipe, air pump leak,

Does anyone know what the metal pipe that runs parallel to the cylinder head directly under the exhaust manifold is?....Mine is leaking and it
is pissing me off...need to source the part for I.D. It has 6 ports off it that go into the head...I think it is some sort of emissions ...pipe eventually leads to the air pump [I think}
My vehicle is a 1982 280ce ...nice car.......good shape too......260000 original k'S
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