The W108 and W109s indicate whether the cars are air or spring suspension cars. A W108 280SEL is exactly the same size as a W109 300SEL. They should also look very similar externally.

You'll find more plush carpeting, burl wood and wood on the doors on a W109 that you may not see on a W108.

Unless your buying a near perfect W109, it wont make a bit of difference whether you buy a w108 or w109 unless your looking for an air suspension car. Both interiors have a capacity for looking rubbish when worn.

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With best regards

Al