All Benz engines are interference engines.

Whether or not you replace that rail would depend on how much vibration you thing not having it in place will cause -- the chain isn't going to jump a tooth, but excessive vibration will cause it to fail much faster than normal, and I'm betting it's pretty ancient.

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!