Interesting new problem -- after 200 mile trip, I checked the oil, which had been changed 1 week prior, and discovered I was 1 quart low. After returning home, I brought it to the service station to see if I had sprung a leak, and they had to add an additional quart. Interestingly, there is no indication of a leak and there doesn't appear to be any smoke in the exhaust. Car has 100,000 miles and has never burned any oil, although it has had its fair share of other interesting problems.

Any ideas on what this problem could be?