[ciwhamc]

OK so what reason do you think they lowered the mileage between oil changes from 15 to 10k?

Did winters get worse?
Did oil change and suddenly have less life?
Did the motors have any significant changes?

No

After working on cars for 15 years you begin to see patterns . Ever since CBS 15 k oil changes came around I started to see strange problems that had never occurred before. Like bad oil sludge build up. Lists of vanos faults. Noisy valves lifters. You open up and engine with 15k oil changes and see the entire cylinder head coated with oil sludge. Oil not draining out of the head because it can't get past the return hole to the sump. That NEVER HAPPENED on frequently changed oil. I see cars come in 5 QTS low on oil. The oil sensor still reading full. It then has to be replaced because I can't clean it without damage.

If you think that your engine likes running 5 QTS low on oil. Remind me to never buy your cars used.