Here it is.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1988-Mercedes--Benz-300se-Climate--Control&yearid=1988%40%401988&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6214%3AMBC%7C1513%3AED%7C10000012%40%40300SE&catid=242213%40%40Climate+Control&subcatid=242328@@Mono+Valve+Repair+Kit&mode=PA