Recently I smoked my Chevy 305 engine looking for vacuum leaks. I found a little smoke coming out of the stem seal in the base of the EGR valve. The diaphragm is ok and holds vacuum. I searched online and did not find much info about it. Only thing I found was that some Turbo Buick guy had trouble with boost leaking out of the stem seal on his EGR valve. Not sure how well the stem seal is supposed to seal for EGR valves?