It is doubtful both problems are connected. My guess is that the vane is in the heat exchanger. just remove the end cap where the raw water side enters. If you don't find it there, then it has to be in the hose between the exhanger and raw water pump. You should fix it, as eventually it could lead to a restriction and overheating.
If the leak is near the front of the engine, it may be the seals on the circulation pump. There should be a weep hole on the bottom behind the pully. Older Yanmar's had problems with plastic fittings for the block drain locations, but I'm guessing yours is new enough to have metal fittings. that said, you may want to make sure those drain petcocks are all closed snugly, just becareful not to overtighten.