Yes, it runs fine. I am asking because I thought this was odd that it didn't happen with my other E3's, nor have I seen it on any other AR I have ever owned. One of my other E3's was a "back up" and didn't get shot often. That one had a light grey parked GB like this one and it never showed any sign of discoloration. I sold it because it just wasn't getting used. The other, my first E3 upper, was one of the very early ones and had a dark grey parked GB. Never noticed any changes at all with that one. Much like a standard FSB, it never showed any sign of discoloration.
I'm curious just how "normal" this is. I see alot of pics of E3's, but they are usually taken when the rifles are new and I have not seen others that look like mine. I figure that there are enough guys around here shooting these that I might be able to get feedback from several people to see if this really is a common thing.