This thread has a picture (and part #) of the filter locations.
http://www.peachparts.com/shopforum/showthread.php?threadid=8950
Also, this company has replacement filters that are upgraded from particle/dust only to particle with activated charcoal as well. they are the only dual type filter I have seen that is like the new models. I don't know how well they work, never tried them as my car has zero filters.
http://web.sunup.com.tw/LYCON/lycon21.htm
__________________
John
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