I'm doing a valve spring replacement on a set of 452 heads. I've already done the machine work for the positive stop seals. Reading info here and there, some are leaving the seals off of the exhaust valve. The fact being, the ps seals do such a good job and the valve doesn't get lubrication from the top, like the intake that's under vacuum. A practice thats done mainly for drag racing applications. So on a street driven engine, what's being used, ps seals and just use gas additives to make sure the exhaust valve is getting lubricated? Is there a ps seal for exhaust valves?