So I must have lost my M12 bit in the mists of time, which is odd, as I still have the 27mm deep socket for removing injectors.
So I picked up a set of star bits, M6,8,10,12 and as today got above freezing, I started pulling the engine apart. When I got the valve cover off, and went to do the head bolts, I was surprised to find the M12 didn't fit right. After a lot of struggling, and mild persuasion (couldn't find my mallet so had to be careful) I got the first bolt out, none of the others seemed to want to co-operate. So I took the bolt with me back to the auto store, we futzed around and found a T-55 was the best fit for it BUT I was nervous that it was too wide a socket and wouldn't fit behind the bearing caps, so I got another of the same set, and the M12 in that fit better, though not as nicely as the T-55.
So what does the modern VW diesel enthusiast use to remove his head bolts nowadays? Should I just get myself a T-55 in a narrower socket as well, and have a choice?