Very strange that this thread hasn't been replied yet...

You can do a search (search button in the right top of your screen) about the dash lights and you will find a lot of different opinions and solutions...but basically you van take out the dash cluster with two (MB specific) hooks while taking care not to damage the dash and to pull the speedo cable to much. Put your hand behind the cluster to unscrew the speedo cable (don't pull the cable too much or you will experience a vibrating needle afterwards), take out the cluster a little further after the speedo cable is disconnected and take off the plugs. Take out the dash cluster completely and change the bulbs.
You can try to remove the lower dash panel, release the flexible ventilation hose over the steering column, get your hand up to unscrew the speedo cable and push out the dash cluster to the front...

Are you sure that he rear window motor is broken or is there any chance that the switch is worn???

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)