oil, gas slick when running

I have a 1984 - 2001. Owned it for 6 years, Great boat, great condition, runs very well. 1200 hours on the motor. Fresh water only, used in Winnipesaukee, NH - early mornings for skiing.   This season I am noticing an oil slick (or gas, tranny fluid) in the water behind the boat when the motor is running - presumably from the exhaust - and it seems to be getting worse. I have added a quart of oil which is typical for a season for me. Oil on the dipstick looks clean, no water or cloudiness, Tranny fluid is also clean, correct color, no water / cloudiness. all 8 plugs look clean, not fouled or wet - no gas smell. Advice from local mechanics is to just run it, which makes sense. That said, does anyone have any advice on what this might be and ways to diagnose it? Thank you very much in advance for your time.

Doug K
New Hampshire

Thank you,
Yes, the carb was rebuilt 3 years ago. This would mean its fuel in the water, correct? A buddy of mine said it was fuel when we were skiing a couple weeks ago because of how it "popped" / appeared volatile when it was on the surface.

what is the best way to check the choke butterfly, just pull the flame arrester and look ?

This would be much better news than oil. Is it possible to post video clips?

thanks
Doug

thanks 8122pbrainard -
I've been checking the tranny fluid level - wondering if this is a possible source. I had the tranny rebuilt 2 years ago, but did not change the cooler, which I presume is original and possibly corroded...would water also go into the trans fluid or not due to it being on the suction (low pressure) side of the raw water pump?
So far it looks like the level is correct and fluid is still red and clear - but this could easily be a slow leak. Thanks for the input,
Doug

Doug,
Correct that since the cooler is on the suction side of the RWP, ATF can be sucked into the cooling. Water can also get into the trans from when the trans cools, the trans vent isn't the best and then there's a partial vacuum created. Yes, keep an eye on both the trans level and the color. It takes a pretty decent amount of water in the ATF to turn it pink. My understanding is the ATF has additives that absorb some water.

You could also pull the cooler, rig up some fittings, apply some air pressure and with the cooler under water, run a pressure check looking for bubbles.