I came to the same conclusion so I called Generac tech support. The guy explained that the break-in oil was simply good ol’ non-synthetic like we put in our cars 30+ years ago. At two years I changed it myself and now two years after that I just had the 25 hour service performed by factory authorized dealer. I was 4 hours early but again after a call to Generac they said it was close enough.The reason being if it takes a few years to get to 25 hours, the break in oil is still in there and they said it could get thick.