Oil consumption

I have a 2005 Buick LaCrosse with slightly over 17,000 miles which I bought new. It is equipped with the 3.8L V6 engine. Since it was new, it has used approximately 1/2 quart of oil per 1000 miles, and I have the oil changed every 3000 miles. I mentioned it at the first oil change, because the low oil level indicator came on. The dealer said that the oil pan was defective, ordered a new one, and replaced it at 4000 miles under warranty. Since there was no evidence of leakage I was sceptical of their diagnosis. The car doesn't leak, or smoke, but it continues to use oil at the same rate, and has done this consistently in the two years that I have driven it.

When I bring this up to the dealer, they want to perform an oil consumption test, which means that I have to bring the car in every 300 miles so they can record the consumption, which would be very inconvenient for me. Trust me, the car loses 1/2 quart of oil every 1000 miles, and I know this for a fact because I have to add a quart 2000 miles after my oil change.

All that being said, how do I get the attention of GM regarding this issue. I have had other GM vehicals with the same engine, and have never had an oil consumption problem. It doesn't make me want to hang on to the car past the warranty period.