Now that the dust has settled off of Christmas and new years I finally got a new set of calipers and measure the bolts that I have. They all measure at 8.3mm. Per figure 03-1/5 In the linked thread above that looks like a good measurement for the bolts to be reused.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"