I have an 07 R18 and have used Mobil 1 and OEM filter since its first change at 5k miles. OCI's are every 5k miles and I'm now approaching 40k miles. I know it's not a lot, but since I'm thinking about it, do most people switch from 5-20 (depending on model) to a higher viscosity due to engine age or should you stick with original spec for the life of the car? I assume it all depends on how it's running later on in it's life, but just wondering if there was a rule of thumb. I'm sure a lot people are up around 100k miles by now, so just wondering what your findings have been. Thanks!