long and short, you heard wrong.
there's only one sensor you should worry about and it's the only one shooting into the bellhousing. it's right above the starter and is a total PITA to get out and back in on a CIS M104. ask me how i know.
the one you should be looking for is this one available here at fastlane:
http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1992@@1992&makeid=63@@MERCEDES+BENZ@@X&modelid=6176%3AMBC|1498%3AED|10000018@@300CE&keyword=crank@@crank&catid=All@@All&subcatid=P%3A242838@@Crank+Position+Sensor&applicationid=W0133-1715281&mode=PA