First off, Pennzoil synthetic blend TC-W3 is all but smokeless. Available at Wallmart in the Sporting Goods department. I assume you are running 1 pint to 6 gallons of gas (50:1). Second, you might either check the archives herein or Google "decarb". Perform that in your driveway on muffs and the garden hose. Do you do much full throttle running? Can you do much full throttle running on your body of water?
What you see may be gasoline as well as oil. A cleanup of your carbs and possibly fuel pump (kits) may be in order, and if original still in that engine, time for replacements.
Petroleum products obviously float on water. If unrestricted they will settle out to one molecule high. One drop of oil was shown to cover a half acre pond in an experiment I saw once when allowed to settle out which was at the level of one molecule. In short, it doesn't take much to make a slick on the water.
Then take some pictures of the engine with the cowl off, preferably where the whole engine angle would be visible in the picture, but would fill the picture and it must be focused so that detail is visible. If you can't get that close, do the best you can for best focus. I'd like to see a right side, frontal, and left side view of just the powerhead....from the rubber seal where the cowling rests to the flywheel area.
Will wait.