B1 must be removed. B2 can stay in place if all you want to do is replace the B3 discs. When I did this job (3 times now--I have 3 124's with the 722.3xx) I replaced all of the seals and that included the B2 seals.... If I remember correctly, when I ordered the new style B2 seals, one of them was not available in the US and had to come from Germany.

J. M. van Swaay

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1994 E320 Wagon, 230,000 miles
1995 E320 Sedan, 106,000 miles
1994 E500 Sedan, 79,000 miles