The head gasket may have been mis-diagnosed. As the previous poster said, leaks more towards the front come from the u-gasket that's under the upper cover.

Your belt tensioner could be worn, but often times the tensioner bolt is merely striped and the belt can therefore no longer be properly tensioned.

Your valve guides may not be worn at all. This would be determined when replacing valve stem seals, but again, if your leak is from the front of the motor, your head gasket, seals, etc. may be fine.

I'd take the car to another garage and get a second opinion.