2005 Buick Lesabre, 80,000 miles. Having to add oil too frequently between oil changes. 2-3 quarts. Have used Pennzoil Platinum 5-30 as recommended. TSA says these cars could loose oil from exhaust valve seals. Dealer wants to do an oil analysis every 1000 miles over 3-4 thousand miles. It has been a very hot summer in Louisiana and wonder if this oil has high enough viscosity. No oil smoke from exhaust. I would rather use Bob's labs as long as they have the ability to pick up possible valve seals or guide problem. Any help appreciated!