Excessive oil usage

2 years ago, I purchased a rebuilt engine from GM (Goodwrench - 3yr / 50K warranty) and had it installed in my 1992 Bonneville SE (a Buick 3800, non-turbo). It now has 25,000 on it. I normally change the oil twice a year; however, this past September (a month before my normal change timeframe) I noticed that the oil was a full quart low (time to add). I ran a regular based oil, the first change, for 1000 miles. All oil after that has been Mobil 1 (5W-30 or 10W-30, depending on the next 6 months of Texas driving temperatures). After I changed the oil, i've noticed that the oil is now being used at the rate of a quart per 1K miles. This seems excessive to me. This car is my wife's daily driver (about 14 miles, each direction). I know this engine 'sat' somewhere for 5 years, before I purchased it (over the net), as the block had a build date of 2000 on it when I picked it up. I understand that I'll have to take it to the dealer for them to check it out, but was wondering if you knew of any problems with these engines. This was my first rebuilt GM engine that i've had problems with. I've purchased 3 'target' engines from GM previously, and they all worked flawlessly. Specifically, I was wondering if you knew of any thing I should check, before taking it to the dealer (e.G, PCV valve (that was a new acdelco when the engine was installed) or cracked seals around the valves, etc). I should state the obvious, there is no oil sitting in my driveway, so I don't believe it is 'leaking'.