Just a few more comments as I've woken up dead early and have time on my hands...
Your BMW problem is just one of several instances I've come across of what I've been calling late onset oil ring sticking (or LOORS for short). Although facts are hard to come by, this might typically hit you at around the 50,000 mile mark & the primary symptom is a sudden increase in oil consumption (but with no loss of compression or drivability). The cause of the problem is a slow accumulation of gunk in one or more of the oil control rings, its associated tensioner spring and the drain holes which sit under the ring. Typically the oil ring assembly will look like it's been 'glued' into its groove and sit flush with the rings lands. Because the oil control ring no longer performs its scrape and drain function, hydraulic pressure builds-up on the down stroke and forces oil through the top two rings/ring gaps and into the combustion chamber. This problem should rate as extremely severe in that the only known proven solution is to completely dismantle your engine at vast expense to remove and replace the offending rings.
It probably fair to say that LOORS is the engine oil industry's 'dirty little secret'. Although you won't find it on Google, the OEMs and oil companies must be aware that it's happening. However, because it's something that happening OUTSIDE of the warranty period, it's something that's getting no attention whatsoever. It's probably overly cynical of me to say it, but I suspect the OEMs regard anyone with LOORS as a potential new sale, not an existing customer that needs helping out. It's interesting to contrast LOORS with LSPI which could potentially happen inside the warranty period. LSPI is getting a massive amount of attention that is wholly disproportionate to the actual risks of it happening!
IMO, LOORS is happening because of the confluence of several factors...
First is the move to ever thinner, synthetic, wide cross-grade oils. Compared to an old 20W50 mineral, you're generally looking at much higher oil volatility, higher VII polymer loadings and worse base oil solvency. The impact of high volatility is the real killer as it potentially loads up the PCV system with oil 'carry-over' as opposed to the fuel & water it was originally conceived to deal with. I can't prove it but all my instincts tell me that the source of the gunk that's causing oil rings to stick is burnt PCV oil and not the products of 'traditional' oil oxidation.
I think a second factor is that some OEMs have been pushing the bore/piston/rings design envelope to achieve certain goals (lower friction, more power, better FE & less emissions) without due regard as to how this might in turn impact on long-term deposit formation. I think certain OEMs are more guilty of this than others (yes Fritz, I'm looking at YOU!). In my bones I can't but think that the basic scientific limits on what can be done are increasingly being substituted for limits based on 'what we think we can get away with'.
The last factor that I'd say has allowed LOORS to develop is what I'll call The Engine Test Mentality. There was probably once a time when oils were judged on what they could do. However over the decades this has morphed into judging an oil on what tests it can pass with no regard whatsoever as to how it might fare in the field. When BobbyDavro and his ilk talk about 'better' oils, what they are actually talking about is an oil that has managed to negotiate it's way through the obstacle course of tests that are required to obtain some kind of 'approval'. By their very nature, tests are invariably 'one-off' tests that in some way relate to one very severe OCI. And there's the problem! There's almost nothing in the testing protocols that covers problems which may develop CUMULATIVELY over several oil change cycles...something perhaps like LOORS...
Ah, dawn is breaking. Time for coffee at last...