Interesting - - The late 230SL diagram shows the O-ring support bracket and O-ring, but the EPC parts diagram for the 280SL shows the O-ring, but not the bracket. Alfred shows the shop manual diagram with a picture of the 280SL support bracket and O-ring.
Now -- my car is a 1971 280SL which I have owned since 1978. The rear axle has not been worked on previously. The assembly paint is still on the bolt attached to the rear axle supportt bracket 7, but there is no O-ring support bracket hanging down from that rear axle top support bracket 7. What I do see is about 1/3 of the original O-ring hanging down behind the rear axle support bracket??
I guess I will do what seems right and cut something that matches the shop manual diagram from tin.