Yep. Follow the maintenance minder (whatever it’s called on the mini) and use the approved oil. If your boyfriend wants it to be maintained to a higher standard, let him buy the approved oil (MAKE SURE IT IS THE APPROVED FLUID - OIL IS NOT JUST OIL ANYMORE in all cases = ask VW/Audi around 2000/2002) and have him do intermediate changes as he sees fit.
Is there any particular reason why he feels the need to have mastery over the maintenance of this machine?