A quick check for valve seals while driving is to hold the car in a lower gear, accelerate the car up to about 3500 rpm, let off the throttle for a few seconds then hit the throttle. If you see a puff of blue smoke (not from the tires!), the valve seals have allowed oil to be pulled past the guides by the high vacuum in the cylinder during off-throttle, then the oil is burned when you get back on it. Oil past the rings is a continual smoking under throttle.