Some sites say that even later model 123s have annualar axles. But not the case on my 85 300D. So best to have look at diff end to see if the axle is connected with a bolted flange.

After looking at all options, seemed to me that buying a pair of new aftermarket axles was about same or lower cost as flex boots plus tools. Later, I might reboot the originals and keep them as spares.

But for now, I filled cracks and coated with 3M 5200 high strength polyurethane adhesive sealant. Allowed time for full cure after several coats. So far so good after a month or two.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5