The seal is a consumable part, just like the spark plug or eventually the rings in the cylinder. I WOULD NOT ever use a permanent "glue" like JB Weld. A properly sized crankshaft seal is supposed to be a tight press fit. It will not come out under normal engine operation. If your seal is loose, it is bad. If a new seal isn't a tight press fit (with a tool), then there is something else wrong with your crankcase.