Engine has done 70,000 miles - regularly dealer serviced but is now losing water at the rate of half a liter for every 100 miles. No visible water leaks, VW have pressure tested it and cannot find anything .Have replaced pressure water bottle which had hairline cracks but the problem is still there. Oil not contaminated. I assume that it must be a porous (?) head gasket . Exhaust emissions look normal. Has anybody experienced similar? And what was the solution ? Love the car but may be it is time for it to go if the solution is expensive to fix...