I've had another session on my manifold today. I've drilled it where the bolts had snapped off where the EGR blanking plate goes. I've managed to tap them to 6mm too by putting the tap in one of those tap wrenches that looks like a drill chuck and easing it round a few degrees at a time with a Mole wrench, hoping it won't snap off in the manifold. It feels like I've got a decent amount of thread going on in there and have put the blanking plate back in with hex head bolts instead of the Allen screws that were on before. It took a while, but compared to the time it would probably take to get the manifold off (which would involve taking out ancillaries like the air conditioning pump and parts of the cooling system) it was probably worth doing it in situ. I don't think I've got the holes exactly centred on the original bolts, but it only has to hold a little plate on - it's not as if it's a main bearing cap. The engine has its performance back now. it's surprising what a bit of pressure leakage upstream of the turbo will do. Then I hosed all the soot out of the engine bay. I think she was running a bit rich. The ECU wouldn't be getting the engine speed expected for a given level of fuelling, so would be increasing the fuel. I shall fill up tomorrow and see just how much extra fuel I've burned coming back from Wales with a leaky manifold compared to normal.