You need to replace the water pump gasket to the block. The oil (coming from above as mention in other post) will eventually degrade the donut rubber gasket. Unless you know for sure that the pump is nearly new (less than a few years old) just replace the pump along with the gaskets that should come with a new/rebuilt pump. Do you want to mess with the pump again in a few years when the pump may fail? Less than $100 for the part, and a pain in the ass to replace.

Good luck.

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Mike in California '90 740ti Wagon- Hydrogeology Field Vehicle