I spoke to an engine builder today who said M1 oil is commonly ran for up to 20k. Then he showed me a bottle of Amsoil that said it's ok to run up to 35,000 (with new oil filters every 12k). That totally blew me away that companies would actually advertise that. Even M1 is advertising that their extended performance synthetic is guaranteed uo to 15,000 right on the front of the bottle. I knew modern synthetics lasted a long time, but not that long. I change my vw 1.8T w/ GC and M1 filters every 5k and I'm beginning to think that is way to often in order for it to be that cost effective. If I could run it for 12k, that would be awesome. Maybe I could do that then run a UOA and see how it's working out. I really hate changing my oil. What would you do?