Sure it's not the sea water pump leaking oil?

I don't believe there is any oil in the sea water pump. I don't think the bolts on the bracket thats bolted to the block would go into any oil pasages.

Yes, there is oil in the sea water pump.

Are you sure?

It depends on which model, The HP 500 has the fuel pump and sea water pump together, There is oil in the fuel pump drive section of it.

Mine is just the one piece plastic unit. Only two water hoses going into it. No fuel pump attached.
Thanks, I wish it was that.

How much room do you have in front of the balancer? I recently had a small sign of oil from behind the balancer and I only have about 10-12" in front of the balancer, shop was able to pull it off and replace the seal part #25, 26-8219471. I would expect though that you would have oil on the balancer if this seal was leaking.... try cleaning the entire area with a degreaser... run the boat and then use a mirror, holding it down below the balancer area to get a better view of the area. This may sound stupid, but you can then toss any type of a white powder in the area which will stick to the oiled area and give you a better visual of where the leak is coming from.... keep us posted of your findings!