The CRUA/CVCA (2.0ll 110kw) have been around since 2013 I believe (maybe even 2012) on the 7 series in Europe. So in a way, the 2015 US version should have had the bugs worked out. Of course, the water pump issue has been known since 2013, so go figure.
Considering how much you are driving, you can certainly get away with long oil change interval.
At this point, it's more important to change the oil filter. Car is still running and doesn't burn oil, impressive!
I had the same thing and thought there could have a been a leak or something. When I did the timing belt, I did not find any leaking seals at all. So yes, i think it is just dirt collecting, from fuel spill, water pump drip, etc.
OK, I see your problem. The camshaft carrier is no longer aligned with the hole, right ?
Then just tighten the sprocket center bolt just enough so you can rotate the camshaft carrier back to the right place, then put the pin in and leave it there.