I have a 97 Cev cavalier and it slowly consumes engine coolant. The leak apperas to be coming from the head gasket but its external only. Is there some sealant that I can apply externally to stop the leak?

No. It could be indicative of a warped aluminum head. I would get it looked at, before any more damage takes place. It will only get worse, the way it is. Fix it the right way and save your engine.