1998 Mercruiser 4.3L raw water cooled alpha drive 220 hours mostly freshwater use. Just changed from single piece to center discharge exhaust mainfolds as a preventative measure. I now notice on start up small amount of white smoke coming out at of discharge. Engine did not do this before manifold change. Also starboard riser is hot to the touch compared to port. I am concerned I have a small leak at the manifold to riser gasket that I cannot see externally.Does anyone have method to test for leaks at the riser/ manifold junction? Otherwise the engine runs fine and does not overheat, does not burn oil and there is no water visable in the oil.<br />Thanks