Approaching 60k on a 02 V6 Toyota Avalon. Went to M1 @ 10k miles to avoid the sludge issue. 5k OCI on 5w30, sometimes with one quart 15w50 when it's hot. So far so good. Pulled valve cover and it was clean. Did one oil analysis @ 40k to see if any issues existed and lab said no. QUESTION IS - Go to GC for duration of vehicle's life or stay with M1. The UOA section shows this engine tough on oil and good OOAs with M1. Couldn't find one with GC. Your thoughts are appreciated.