My Mk1 laguna has been working perfectly for the 9 months that I've had it, but this week the heater stopped working and the engine began to run a little hotter than normal. It also started going through a lot of water. The water doesn't seem to be leaking anywhere as ther are no pools of water under the car. Have checked the oil cap for any furring and there doesn't appear to be any. Is this a case of a possible cracked cylinder or a faulty head gasket. It runs ok but needs a lot of water. Should I stop driving it?