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While BMW having to pay less (make more) for greater service intervals may sees like quite the biased enticement for BMW's largest market, if you as an owner then don't follow BMW's recommendations, but instead run 50% longer, and trade the car in, BMW has so little concern that they will turn around and warrant your engine for the full CPO term. The cost of failure of engines (both in repair costs and loss of reputation) in those cases would be far higher than the savings related to the owners who ask for annual oil changes. So, they have already put their money where their mouth is. On top of the warranty costs, BMW holds the lease residual values in many cases. They are the ones at risk. If engines started cratering, lease values would plummet.
I also don't believe you can ask an oil company for a recommendation on how much of their product you should buy. They were part of the 3000 mile change myth that went on for years. They are motivated to have you buy much more. You need to ask the engine manufacturers, as they are the ones who carry the risk. You can analyze the oil during its useful life, and see if it continues to exhibit the properties it needs, and whether it still has sufficient additives, but those tests have been done, and we know that the oil stands up, apart from those applications that can be judged to be severe service.
You mention synthetic oils and better manufacturing tolerances, but in my mind (mech eng here), what is more important is that the sump is twice the size of many others (giving literally twice the interval) and the engines are ultra low emissions, meaning that there are far fewer byproducts of combustion to contaminate the oil. Engines burning cleaner means the oil stays cleaner. You can filter out metallic particles, but you can't replace the additives that are lost to acids which contaminate the oil.
Let us know what your dealer says when you ask him if there is an SIB on annual oil changes that applies to your diesel.
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2007 X3 3.0si, 6 MT, Premium, White
Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue
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