All TR Buicks came new from Buick with "Kendall" GT-1 in their engines! Why? Kendall is the only pure petroleum base stock oil left on the market today. Valvoline and most all the others are parafin base stock today. Most all the new blends of oils have the sulfur content mostly or all removed because of the EPA wackos! This isn't good for cam lube or upper engine lube. Ring seating doesn't happen during the first oil change if the very hard rings are used, especially moly rings. All the other cars that came with synthetics in the engines are broken in before ever installing the engines in the car, then it is OK. I only use Kendall in both my TRs and 10W30 wt. My engine rebuilder told me not to ever run synthetics in his engine! Why? Ring seating. Your choice. Gene |