took my vw t4 in to garage told him it would start through the day,then all of a sudden it wouldnt start, this been going on for about 6 weeks, he said he check all connections and every thing, said he couldnt find a problem he then said he found some water near the glowplugs he dried it off and it started 5 or 6 times on the trot.he left it for about 2-3 hours went back to it and it wouldnt start again, so i went down and on my way down he phoned me to say it had back fired and your cylinder head has blown, even tho it was running fine when i took it to him just the starting issue, could this be caused by that plese help as im confused...thanks daren....ps it had a rebuilt engine 3 years ago which has done 18,000....