40000Km on an oil change scares the Hell out of me........
I do 12K with Mobil one and only 5-7K with an SM rated dino/synth blend, and even then it comes out looking pretty damn ugly. Sure the oil might still lubricate, but how much carbon, varnish, fuel and particulates can it really absorb till it becomes glue?
I just helped out a friend with an A class Merc that had carbon contamination sensor problems and collapsing oil filters from the long duration oil changes. OEM manufacturers are really pushing the boundaries these days in order to produce "low maintenance" cars that sell, and they do because the "perceived" service cost from long intervals is cheap.
Problem is all the shit from long service intervals is only going to show up once the maintenance plan expires, and what the heck, we'll sell you a new engine or parts then and make more dosh anyway.
You can change oil an filter too often as well, I remember looking at results of oil analysis tests recently that showed the filter only reaches it's maximum efficiency after a few thousand Km. Oddly the oil parameters and particle count were consitently at their most stable about halfway through an oil change.