Are you taking the BMW Castrol to their recommended OCI or 7K

I generally just do a oil change whenever wheels are getting swapped which is not exactly a true mileage indicator but it's somewhere around 5-7K on average.

Any decent oil should be okay at 7K intervals. IMO, just use any oil that meets their HTHS spec. M1 01W40 will work just fine.

I'm inclined to steer you towards Amsoil but that just because I like their stuff. TA, if I recall you tow right ? I use Amsoil 75W110 which is a tad heavier when Warm than OEM spec of 75W90. Some food for thought...