An update to my fellow Opelians. My daily ride Veccy has now hit 327K. I have been carefully watching the head gasket fail yet again. There is an intermittent drible of oil coming from the block and the head below the coolant thermostat. This is the head bolt that was stripped by the stealership. Without going into massive detail the leak occurs when the metals begin to heat or cool (expansion, contraction).

This particular head bolt may need re torque but as you would all be aware the cam would need to be removed. In other words, a new HG would be a better solution as it appears that the 25nm that they reckon should really be 30 by my calculations and then the varying degrees of pressure added.