There are sevrel ways a headgasket can fail. ie coolent in the oil ,pressureizing the coolent,coolent useage etc IMO if compression was getting in the oil ways the build up of pressure in the crankcase would force oil past the oil control ring and burn in the comperssion chamber causeing blue smoke. wash engine off with some degreaser run up have a good look round with a torch. you suspected H.G issue, pop in to a garage an have them carry out a sniffer test. hope this helps