theres nothing wrong with the comp readings pete and they are all pretty similar across the board.
it would only take a slight blow into one cylinder in order for you to lose some coolant, so the one i would suspect could be no4 with a few droplets lying on top of the piston
if you have an old spark plug or adaptor then connect it to compressor airline and set compressor to around 40 psi whilst no 4 is at tdc with valves closed.
remove the radcap and wee if you can see or hear any bubbles in coolant system, if so then the head gasket is leaking on that particular cylinder
it sounds like its only a slight blow at the moment but obviously thats no good and will need sorting.....in the meantime i would just use the car as per normal and just check water a bit more often and top up if necessary, if shes kicking out clouds of white smoke and fowling the plug often then i wouldnt use her anymore untill its sorted as you dont want to risk cracking either the head or block