A not-so-welcome guest spilled heavily-milked coffee inside the grill on the passenger in-door stereo speaker. I have cleaned off the surface with a cloth, in the hope that this would also gently clean the surface directly behind the grill. However, from the driver position, one can see the paths that the streams of coffee took inside the grill. 
For some reason this irks me, while the off-road dings in the exterior do not.
Any suggestions on cleaning this out?
For some reason this irks me, while the off-road dings in the exterior do not.

Any suggestions on cleaning this out?