Just a little update to say that things are a little less mysterious now. I'm really determined not to do a half job this time because I am really quite "done" with this whole issue.
I got the driver's side head off. This is the one with #7 that ingests and burns all the oil. My two heads were obviously built on different stations or something because my passenger side head the rocker stud holes don't break through. However, on the driver's side the really break through hard.
driver's side rocker holes
I didn't think this was the main problem but I didn't like having such a large suction hole especially when it seemed like the threads were proving hard to seal. I knew the holes were so deep there was some good depth to work with. After trying some rubber plugs as seals I realised that the best plug would probably be a solid lump of Right Stuff black RTV. So I put some in the bottom of each rocker hole then screwed in the rocker stud. I wiped off the excess from the inside of the port with my finger. I think it will prove an effectively "blind" hole now.
plugged rocker hole
Nonetheless, my investigation with the vacuum suggested to me that a lot of the oil -- maybe all of it -- was coming in through the headbolt hole side. This was a bit odd since I sleeved these holes last go round. The sleeve is visible from inside the port and looks intact.
Well, I got to shining the light around and I thought I saw something in the sleeve from a certain angle. I had a little bit of the tube stock left over so I was game for driving it out to have a look.
what I saw
I drove it out (which wasn't as easy as you might think since I had loctited it in there) and -- yup -- that would, er, be a problem...
a sleeve with a view
Sam