Your car your - your engine. I change out my BMW LL01 (Castrol BMW Special oil for MINI vehicles) at 12k - half the recomended 25k (kms). I change the Magnatec in my garage queen E38 half way down the service lights and the same with the GTX in my E30 and E23. When was the last time you heard of an engine failure due to too frequent oil changes? My mother still has my father's 1959 Morris Minor wagon (woodie). Guess how often the oil in that car gets changed. I want my cars to last more than my lifetime. Like I said: Your car - your engine. (Also helps if you understand how oil interacts with engine components).
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 White and 1 Light Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i