IMO you went too long for your first change. Should have changed it at 25-3000 and started using full synthetic. From then on no more than 5000 is the way to go. I also believe you should get a catch can installed. Run 93 octane non ethanol if available, better gas mileage and it makes these bad boys perform. Personally I look at the oil life but just to see what it says, I change every 5 with rotate & balance. I have an 18 now in 2 years with no issues. Running it like I stole it and she just keeps on pulling!