So each of the 4 flange bolts broke off. Have the Exhaust off the car, looking at the remaining studs, it would seem that you could just hammer them out right? What size bolts do I need to order as replacements when I put it back together?

Are you at the exhaust manifold or the pipe connection under the rear of the car?

In either event, they should be 8mm ( 5/16" ) and about 60 mm long ( 2 1/2" ) . On the ones I have taken apart, there are square nuts on one side so tapping out will work.

If it's the same as the E420, they are square. They can be hammered out and replaced with new nuts and bolts. Here's what it looks like new (pictures). The nuts install into the collector one way -- with the serrated edges facing up (away from the bolt). The round smooth part faces the bolt.

Attached Thumbnails

     

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Perfect! thanks.