I have been a religious GC user for years with all my cars... from my previous BMWs to my daily beaters. It has kept my engines running quiet/smooth and the oil relatively clean... I'm an absolute believer in it. After being forced to switch to the Mobil 1 0W-40 for my 2009 GT-R and seeing how dirty my first oil change was, I'm now contemplating changing to GC as an alternate oil. However, given that the GT-R specifically calls for M1 0W-40 ("specially designed with the high performance plasma bore engine") and the GC is more of a 0W-30, I'm wondering if this might not be such a good idea. What are your thoughts about this replacement possibility? What are the downsides and pitfalls to watch out for? As always, thanks in advance!