Happened to my '99 GS this past summer too. Everything seemed intact yet I found I was losing coolant, but luckily I caught the problem just in time (no overheating, or any engine damage). I was also puzzled at first as to where the leak was, because I never expected something to leak out from the top (i.e. against gravity). If you're leaking coolant, check the top side grille of the radiator to see if coolant is escaping from between the metal/plastic "teeth" of the radiator. It was also due to age and seasonal changes (spring > summer) as I was told. Paid through the nose at the stealership since I it's my daily driver and don't have a garage to manage a quick fix.