Which automatic?

[v1rotate <v1rotate@xxxxxxxxxxxx>]

Im looking to buy an automatic. I want a
535I...540I...735I(L)...740I...etc. If I stick with 89 or newer will I
avoid the older automatic from the late 80's that wears out at 125k or
so?
What are the designations and which year model has what?
Should I pay the extra for the 8cylinder and suffer the fuel mileage? Is
the "8" much more expensive to maintain (other than 8 spark plugs
instead of 6, yuk yuk)?
Any help with these questions is greatly appreciated.
Dan

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