I just finished rebuilding my '90 325is after 8 years of working on it off and on (mostly off). The last step in the process was to top off the coolant. At this point a slow leak was found at the base of the water pump (see image 1). It's a completely rebuilt engine. It's a new water pump and gasket. All bolts were properly torqued. I am trying to determine what the issue could be before I tear down the engine again. I had the engine hot tanked to clean it. Could this plug be the culprit? Any ideas would be appreciated.