All our MBs since about the mid '70s have had 2 or 3 tapped holes in the parcel shelf (or behind the rear seat or on load area floor in the case of the wagons). They are tapped 5/16" from memory and usually have a black plastic cap (about 25mm or 1" dia.) screwed in when not in use. Maybe this was some unique requirement for Oz deliveries although I'm fairly sure the owner's manual covers it.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.