I replaced the rocker buttons about 50000mi ago when I did my heads. Recently I had one fail and the rocker walked off the side of the valve stem. The engine still ran, just with some popping. I pulled the upper intake and found that there was back pressure from the #8 cyl. After pulling the valve cover off I found the failed button and that the exhaust valve likely wasn't opening as it should. There is slight damage to the valve stem, mostly around the edge and the wear on the rocker doesn't seem out of the ordinary. Has anyone ever dealt with this? I'd love to hear what others may have done. I'm fearing that a head rebuild may be the worst case scenario on a relatively new head. Thanks in advance.