I have removed the head to find that I did indeed fit an MLS gasket. There are no obvious signs of failure.
Today I have cleaned both the head and the block and, subject to further checks, I have found that the head is flat so no need to skim. But the liners are not over 3thou in fact they are 2thou so it looks like I was badly advised back in 2010. I need to sort out a more accurate straight edge to be sure.
Also I have found that 3 of the 4 camshaft seals have failed, that's not very good considering the engine has only done 40k miles