e39 oil consumption

Hi, I have a 2001 BMW 530i with 82k miles, and it recently started consuming oil very rapidly - about 1 quart every 500 miles. I already had a new engine put in (under warranty) at 50k miles, so this engine only has about 30k miles. Gas mileage is fine, there are no leaks that I can readily see, it seems to run fine, I'm not seeing any smoke, etc. Any thoughts?