2002 Q45 Oil smoke when starting

[carnut]

70,000 miles, maintained by the book since new, burns some oil (needs a quart added between 3,750 oil changes, which I'm told is normal). Quaker State 5W30 oil, car in San Francisco CA area.

Blows quite a big - a few feet in diameter, cloud of blue/oil smoke on startup after parked for several hours (e.g. overnight).

1. Would it be valve guides or something simpler like a stuck PCV etc valve?

2. Assuming it's serious, what are the manufacturer's responsibilities in terms of fixing emission problems on such low miles/well maintained, high-end car? The full warranty ended last year, I did not bother to claim it as the smoke was very small a year ago (but I realize that those engines can be quite oil burners, I talked to a guy who had the 2002 Q45 engine replaced under warranty for excessive oil consumption). Are there any emission warranties/responsibilities, specially in California?

thanks for your help

George