If it is like my '94 850 sedan or my in-law's '95 850 sedan (and I think it is) there's a rug flap covering the back of the tail light assembly. Fold the rug flap back. The tail light assembly is held in place by two plastic lever-like things at left and right edges of the assembly. Gently pull the levers toward each other (easy to do one-handed since the assembly is about as wide as your fingers can comfortably stretch), and the assembly should pop out into your hand. Push the bulb slightly into the socket, 1/8 turn to left (I think) and the bulb comes out. All auto parts stores stock those bulbs.

Easy and quick to do, requires no tools -- and you can do the repair in the auto parts store parking lot!
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-- Bruce / '82 244 (315k miles!), '86 745, '87 760Ti, '94 854