I don't have any definitive info.... but I believe that the MB factory shop manual on climate control suggests putting a new manifold on when replacing the compressor... there are at least two reasons which come to my mind... one is that some of them have a filter in them which is not cleanable... so a black death at any point in your car's life might cause there to be a restriction there... or they found out that the manifold warps under the constant hydraulic pounding it gets and instead of saying they made it wrong they just post the procedure as ' requires replacement' ... Greg