I recently had new carpets installed in my '79 450SL, and they installed a new carpet piece there, also gave me a spare. It has trim around the edges, and was there when the car came from the factory. Mine doesn't have the velcro, it just fits in the little slot around the bottom edge.

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C