Omega coolant leak ?

I'm having another omega coolant problem. About 3 years ago head gasket went at about 89k. Had it done and fine for 3 years/27k miles. Now I'm losing coolant, about 1 pint/10miles. No drips founds under car when parked up. Footwells dry. No water coming out of exhaust or contaminated lambda sensor as happened before with head gasket problem. Also fuel consumption has dropped from typical 25 to 19mpg. Can anyone give me an idea what might be happening or what to look for ? I wouldn't have thought the head gasket has gone again so quickly plus the symptoms are different this time ? Regards Tony