Years ago my Mom always used Quaker State in her Buick since new. Eventually the motor developed some problems and my brothers and I tore it down. Whew, what a mess the top end was. Looked like it was filled with ashes or something, rockers all glued together and stuff, quite ugly. I swore I'd never use the Q again after that!
In all fairness, she never did drive faster 40 or 50 mph and a LOT of 'milk runs'.