Anyone ever had this problem? My low coolant level light has been on for a while now (couple of months), even though I know it's got plenty in it. Finally got around to looking at it this past weekend, and found that the little cork that floats up and down in the reservoir doesn't float. It isn't stuck (I could move it around with a pair of needle-nosed pliers), it just doesn't stay floating in the water. Any advice?