Depending upon what year yours is, it may or may not be available as a separate part. Early M102s had a metal oil separator screwed to the inside of the valve cover (rocker cover, cam cover, call it what you like) that is available as a separate part (but probably would never need replacing). Late M102s had a plastic oil separator (also held in with screws) that becomes brittle and cracks up with age (which is what I suspect yours has). This unit is not available separately as a spare part (makes a lot of sense... not!). With a broken oil separator in my '90 190E-2.3 (and a warped valve cover with flaking black finish) I was facing a cost of over AUD$700 for a new valve cover (including oil separator). I tried the earlier metal oil separator only to find that it does not fit my late valve cover! Any second hand valve covers were no better than mine.

In the end, I spent a whole Saturday afternoon fabricating a copy of the plastic oil separator from sheet metal (quite a fiddly job requiring cutting, shaping and brazing skills). While the valve cover was off I also bead-blasted all the flaking finish from it and re-finished it with high temperature engine enamel. When re-fitting the valve cover with a new gasket, a fillet of black gasket silicone sealant in the groove took up the variations caused by the warped cover. To this day my fabricated oil separator is working fine, my painted finish is holding on and the gasket has not leaked a drop of oil. Yes, a lot of work but a lot less cost than a new valve cover.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.