2008 Supra Launch 21V Drain Question

[CDWindman]

Hi. We are the proud new owners of a 2008 Supra Launch 21V. It is our first boat and we are thrilled with it. It has about 450 hours on it and has run perfectly all summer. I do have one question though. When I remove the drain plug on the back of the boat the water that drains out has a little bit of oil in it. I have just assumed that there might have been a little oil in there from an event of the past owner because it is an 11 year old boat and over time there could have been a little oil in the area that the drain plug on the back drains. It is not enough to discolor the water, however when it drains I can see the a little of the oil in water color on the ground. There is no oil in the water that is pumped out of the bilge pump. Also, there is no current loss of oil. Any help would be great. Thanks.