take a stiff bristled tooth brush heat the handle about 1" back from the head and bend it to an angle, then take some scissors and randomly snip in the bristles so they vary in length by at least the depth of the grain you are trying to clean...
Then you can hold it between your thumb and index finger with the tip of your index finger work in small circles clockwise then again counterclockwise the bristles pick away at the dirt... using anymore pressure rolls the ends of the bristles over and they are rendered pretty much useless...
Wipe with a CLEAN white rag and when there is no more brown residue you are done.
I don't know that I have ever found TRULY clean interior in a purported "clean" car.
I've got one crazier... check out the 69 Camaro dash pad - top directly above the clock or center fuel-
__________________
~JAG~
NCRS#65120
68 GTO HO 4 spd Alpine Blue /Parchment 2 owner car
#21783 71 Corvette LT1 45k miles Orig paint - Brandshatch Green - National Top Flight - last known 71 LT1 built.
71 Corvette LT1 42k miles Original paint - Black - black leather - only black LT1 known to exist.
NUMEROUS Lemans blue Camaros,
Monza Red and Daytona Yellow Corvettes
& a Chevelle or two...
Survivors, restored cars, & other photos
https://picasaweb.google.com/lh/myphotos