I just unboxed a brand new FMF Q4 pipe for my WR, and it has a dent in the same spot. Looks like it's supposed to be there. Even if it was a ding in your pipe, it wouldn't make that much difference in the performance.
As far as the gap in the header, if the PO sealed it when he assembled it, and it's not leaking, -I- wouldn't worry about it.