Oil leak spotted - but what is it?

Hi. Last week I posted a question regarding an oil leak on my 95 E320. Well, after a good cleaning I believe that I have spotted the source of the
leak - but I have no idea what it is. The culprit (or the location where the oil seems to be collecting first) is located on the forward, left-hand (when facing the engine from the front of the car) portion of the engine. It is a brass-colored rectangle (approx 1/2" on each side) that is situated just ahead of and below the exhaust manifold and behind a 3" long metal tube (approx 1" in diameter - the tube itself goes nowhere and terminates with a bolt) and what seems to be the mounting bracket for what I believe is the power steering pump (not sure on this one).
What is this device?
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