I have an old (1990) GMC Rally van that gives out a little puff of white smoke on start-up. I suspect the gaskets dried-out as it only has 120,000 km (75,000 miles) on it. Good van for hauling kayaks and bikes around, but I don't want to spend a fortune to repair it as I paid about 1K for it a few years ago. So, what do you guys think of the "miracle in a bottle" head gasket sealers? Worth a try? Anyone has first-hand experience with the stuff? Any recommendations on the brand? Thx.