Has your exhaust been blowing white smoke too? It may be something like needing a head gasket replacement, I know my '61 needed to have the head re-milled and after that I had no problems with a similar issue, but breaking your engine down to parade rest is a personal decision, if you do this, at least you know that you have eliminated all questions as to what it could be. If you decide to pick and choose, you get what you invest into your engine. I am certain that someone here has dealt with this, I am interested to see what the prognosis is.