My recommendation is buy a set of used coils on ebay for cheap.

I bought a set of 6 Bremi coils for my 1998 528i (E39) for $50, so less than $10/each.
They sit in my garage waiting to be used. At 150K, my 1998 528i is still on original coils.

Used coils on ebay are usually stock BMW coils, they are cheap and you can keep some in the trunk as spare.

Just remove the cosmetic cover (10-mm bolts) and store the cosmetic cover in the trunk, this way you have quick access to the coils.

PS: replace only the coil that is bad.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT