My 261 has bad exhaust valve seals. It uses a quart every 300 miles or so and doesn't foul the plugs because the oil is going right out into the exhaust manifold and burning off, and you don't notice unless you get right up to the tail pipe and sniff. It only shows up blue if its been sitting at idle for a while or going down a long hill. I was going to fix it but I'm swapping a GMC 302 into the truck.
