I have a 2010 Toyota Prius Hybrid with 235,000 miles. Recently it started running rough so I brought it to a Toyota service center near me. After 1 hr. of diagnosis, they reported they suspect a head gasket problem based on oil being 2 quarts down and coolant reservoir being empty. It occurred when temperatures in my region where sub zero for prolonged period of time and about 2,500 miles since my last regularly changed oil/filter (historically changed every 5,000 with synthetic oil). I was surprised because the car ran perfectly before. Under the assumption it is a head gasket issue (not leaking, but slowly burning), will one of the Sea Foam products help seal the head gasket? If so, which product is best and do I apply it to the oil or coolant?