Denting/Deforming the mouth of the brass is normal for HK weapons without port buffers.I really don't know about weapons with port buffers as I've never wanted to put one on because if you ever take it off it will scratch the hell out of your finish––––that was before I saw this one that appears to be made out of plastic which is good in this case.
As far as the ejection issue have you tried sliding the buffer forwards or back to see if that makes a difference?retrodog and Osprey21 are the 2 best HK guys here,they can tell you if this ejection problem is normal if you have the port buffer.