I'll have to check on my brother's SDL, but typically there is an access panel inside the wheel well on the back side. Several screws and the panel comes out. May not be true on the W126, I'll look.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!