The instrument cluster can be removed to replace the bulb. Fairly easy once you get the hang of it. Basically:
Remove the square trim panels on the right of the cluster, they snap out.
Remove the knobs and then the trim panels around the light switches on the left side.
There are four screws holding the inst.assy into the dash. Notice the 2 on left also hold a reinforcing plate for the light switch shafts.
I have found removing the trim plate over the steering column helps, 2 screws.
Hard Part, unplugging the connectors to the back of the assy, careful of the one to the speedo. But if you break off the piece that holds it, it will still go back together.
Replace bulb:

Might be a good idea to get a Bentley manual.
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84 242Ti IPD bars&springs, 89 745 16v M46 IPD bars, 89 744 16v M46 IPD bars, 93 945 Turbo AW71, 91 245SE AW70 IPD bars, 93 245 CLassic M47