You can remove the cap (three bolts visable outside(allen heads, one inside the cap) and clean it off gently with a brass tooth brush. Once clean, just put a VERY THIN layer of grease over the area... Make sure its nice and clean before re-installing
Don't damage the sealing gasket/rubber.
Its really not that bad and not unusual.
Once the picture's open, double click again and it'll enlarge further..
I usually use silicone dielectric grease, since it's ungodly sticky, but clear so it's not a nasty mess if you accidentally get it on something.
Townsend is definitely right about it not being a huge deal. I've seen 30+ year old bikes that have the same issue, and I guarantee you it didn't just start recently. Might as well take some simple steps to fix and prevent it though.