It could be that your rings are going. Have you done a compression/leak down test?

The 3.0s do burn oil, but it sounds like something is up. One band aid solution would be to step up to a slightly thicker blend like 10-40 or 10-50.

Check the plugs, black gunk means you're burning the stuff.

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2002 X5 4.6is - Titanium Silver / Black Alcantara - Dinan Stage 2 - Bilstein/Eibach - Brembo BBK ----SOLD---
1993 318i - Brilliantrot / Tan - bone stock daily driver