Originally Posted by def
Your photos suggest that there was wet carbon present in the combustion chambers. This could be due to several factors. How do the piston tops look? Same wet carbon? If so, I would continue to look for a source for oil in the combustion chambers.
New exhaust valves and stem seals with a valve job according to the specs in the BMW REProm. One exhaust seat looks like it has a nick in it. Take the heads to an expert who knows how to shrink new valve seats into the alloy heads and perform the multi angle valve seat grinding.
My photos? I did not post any.