+1 on regular servicing. I'm in trouble on the E34 forum for suggesting double oil changes but don't reset the SI. Like I told them your car; your engine. I know how I treat mine and can only pass that info to you. Service your 7 and it will love you back and not let you down.
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i