I've got an '27 260E and that stooooopid light came on every other time I drove the car when I first got it. I found it was mostly loose/corroded connections inside the tail lights. A lot of wiggling of bulbs did the trick. I also very slightly bent some center contacts to add a bit more pressure to the bulbs' center contacts.

A way to figure out which bulb is not working: turn on every light switch one at a time, including the brake pedal. The warning light will come on when you hit the lucky switch. If it only comes on for a couple of seconds, it's probably a loose contact.

There is hope,

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Norm in NJ
Next oil change at 230,000miles