Lifters and Oiling

I don't appear to fuel mixed with any other fluids. Oil and coolant seem normal.


However, based on RustyRatRod's question, I rechecked the oil level. I'm a quart below max; which is a quart lower than expected.

The light-coming-on-going-down-a-hill incident was 5 weeks ago. That day, I check the oil level. It took two quarts to get back to the 'Max' level line. Today, I find I'm just a bit under the 'Add'. I can't think of where the oil could have gone except burning it. My exhaust isn't particularly black. Is this something I can check the spark-plug tips for?

EDIT: Thinking about it, I filled the oil with the car tilted toward the passenger side, engine hot. Checking it just now, it's titled backward and cold. That would definately account for at least some of the missing oil. I'll still see about checking the plugs.