"Also, just so you know, the bulb indicator idiot light measures differences in between the bulbs from one side to the other, and it is very sensitive. So if you ever replace a bulb, you have to replace its mate on the other side (ideally with the same brand of bulb)".

I don't like to disagree, but in my experience (14+ years and many 240s), this is something of an overstatement, and could result in a lot of wasted effort (and bulbs) if followed religiously.

I replaced a friend's tail light bulb only yesterday, using the first bulb at hand, and there was no false BFS warning light.

While I do agree that "mismatches" can occur—and usually require some bulb swapping to cure—in most cases all I have had to do was replace the dead bulb.

So that's what I'd advise first, adding that the other side may need attention. But not always.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.