Ebay is really my source of the data, I didn't pull a PN on my unit....hmm, actually I'm finding more than 2 PNs. Maybe this is just a case of MB resolving DMS issues with components? I can't find good info on the board about compatibility.
My PN...
should be 124 83 00 285 it looks like.
1986 89 Mercedes W124 Dash Climate Control Unit 1248300285 | eBay
1992 95 Mercedes W124 Dash Climate Control Unit 1248303385 | eBay