I took the easy way out when my 380 water pump leaked. I removed the pulley the backed the bottom bolt out enough to get at it with a hack saw. I cut it off close to the water pump's ear and took the pump off.

I like the idea of using a piece of all thread and a nut for reassembly but I didn't think of that. I notched the bottom ear of the water pump and slid it down on a new bolt.

That was seven or eight years ago. No leaks yet.

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84 300SD
85 380SE
83 528e
95 318ic