W126 300SDL . Aux water pump next to monovalve- can it be repaired/sealed tested?

[werminghausen]

I bought an old aux. el. water pump. I don't know the condition...impeller turns easily but I don't know the condition...it might leak for instance.
I removed the 4 screws and the plastic housing comes off. The O- ring is old ...original ring has maybe size 38 x 2mm.
I'd need at least a new o-ring here ...not sure about the shaft seal.
To get to the shaft seal I would need to remove the impeller. But the impeller is not supposed to be removed as it is on a knurled shaft.
Anyhow with a new o-ring I could at least try to test the pumps for pressure of 1.5 -2 bar (pressure of the cooling system)

Has anyone done rebuilding of this pump?

Also the original plug is missing as you see in the picture. Is a plug available from MB and who has the part number?

Best, Martin