I suppose it is too late for a break in oil.. Lesson learned. I will continue to use Penn until they stop making it... Now, what to use in my 85 GT witht he rebuilt 5.0? It has a roller cam and is completely rebuilt. Nothing fancy, just rebuilt to stock as I wanted to keep it all stock. It has CATs unlike my CJ5 with the 283. I am guessing some sort of break in oil..then synthetic?