After removing the dash and center console, you can follow these steps to clean the airbox:
How To Disassemble A W123 Manual Airbox Photos by daw_two | Photobucket

Also, removing the seats, floor carpets and scrubbing with soap and water helps.

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daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
No longer selling Cluster Needles Paint
No longer selling New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more