So today when I took off my exhaust manifold, I did a quick visual inspection of the valves, and I had noticed that all of them have this weird black grease on top of them all in the same location right where the groove is on top. Is this normal or can I just wipe it off and let it be?

Sorry no pictures, I had to be at a certain angle to see it and camera wont focus on the valve.

 

Air + fuel burning up inside the chamber causing exhaust gases to be formed... I'd say that's normal...

 

I thought so, just wasnt sure if it was a sign of running rich or whatever. Thanks!