This Bosch filter site lists the filters on the German model S class as being behind the glove box. http://aa.bosch.de/advastaboschaa/Product.jsp?prod_id=91&ccat_id=37&language=en-GB&mtype=P&publication=1&flash=
(Click on 'vehicle specific installation' button at bottom of page.) Some older threads on searching for 'Cabin Filter' indicate that there may be an additional charcol cannister filter?
Maybe a US 140 owner can kick in.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E