PartsShop (see headers at top of page) lists 2 filters for 92 400e.

http://catalog.eautopartscatalog.com/mercedesshop/wizard.jsp?partner=mercedesshop&year=1992&make=MB&model=400-E-001&category=R&part=ACC+Cabin+Filter

I posted a thread detailing ACC filter replacement for W202 at: http://www.peachparts.com/shopforum/showthread.php?threadid=53623

your 400 may be similar installation.

hope that helps. - benton