To me it looks like the seal between the seawater pump body and engine block has failed - black fraying deposit close to mounting surface / seam. The gear on the "oil side" of the pump is rotating fast and most likely spinning oil around the housing.
If this is true, oil droplets could also "spray" upwards. Have you looked at the pump area while the engine is running? Clean all leak / stains out, put some white paper tissues around the engine and find the first droplets?
BR,
Tommi
s/y Anniina