What is it?
 

It's in the oil line in front of the filter as you face the car(72 4.5). Looks like a disk with 6 10mm bolts thru it that hold it together. Got a rubber diaphram between the two halfs of the disk. Could be a oil pressure damper? Mine is leaking oil like crazy. Tried to tighten it to no avail. I'm afraid to crack it if I tighten it more. What to do? I'd get a new one if I knew what to ask for.

there is a replaceable rubber diapram inside, it is mercedes number
116-187-03-92, that should stop the leak

Thanks Ray.

Yes, it's a damper. While you're down there, be sure to use flare wrenches and counter hold each piece. There are a pair of small metal pipes that are easy to bend. You'll discover that a thin 7/8" (22mm) open end will be needed as a counter-hold. Sears has a nice set of thin wrenches for the ocassion.

You might want to get a salvage yard set of hoses and have a shop refit them with new rubber and install those instead.

-CTH