Are you planning on taking the entire dash out? Probably not necessary. On my w126 I didn't have to do all that, can't say much for the w123.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth