my daughters car is a 97 sc1, noticed over the last few months of having to add a little coolant every few weeks. there are no signs of leakage, so i presume it is getting burned. also notice here lately that the car starts rough then clears after a short time. i suspect the headgasket is starting to give up. car runs great after about 15-30 seconds and doesn't heat up. has anybody had this experience, and what kind of $ for a headgasket replace?