Valves can stick even with lubrication if the clearance is too tight. We no longer use intake seals unless the customer requires them and then we add a little to the clearance. Seals on the exhaust are not used for two reasons; the relatively low valve angle does not readily collect oil at the guide, and, even if a small amount got past the guide it will just go out the exhaust. Since you have the heads off you should verify proper stem clearance on all valves. If you have any concerns then a little extra won't kill the life of the engine. .