Oily film out of exhaust

I wouldn't rule out leaking injector(s) either.

I had same filmy issue from stbd engine. Ran injector cleaner and it cleared it up.

Although difficult to tell just from photos, but appears to be diesel vs lube oil. Lube oil tends to stay together more and form circular pattern. Diesel is lighter and thinner and usually leads to the ribbon type streaking you are seeing.

Good point, CR.
For some reason, I had in mind that it happened upon cold start, rather than after shutdown (as the OP actually said).
On the other hand, if I understand correctly his post #7, he did experience the same leak also upon cold start, which is indeed a scenario that might point to injectors.
But I agree with the OP that it would be a weird coincidence if it never happened in the past, and out of the blue it happens on both engines...

I'm going to go out on a limb here and call it on the injectors or fuel cooler. Buildup in the exhaust water during idle running during docking, etc, leaves residue in the exhaust that slowly washes out in a manner where a little goes a very long way. Let the boat sit, and it completes its discharge. Fire it up again, and you're re-introducing the unburned fuel to the exhaust water. So, bad low idle spray or drip from an injector that produces unburned fuel through the valves, or some small amount of fuel weeping within the fuel coolers. Fuel coolers seems much less likely to be happening on both engines at the same time. So injectors...

I get this on my '43 with Volvo TamD 480's. It happens with cold weather. If the water temp drops blow about 50 degrees I get a slight sheen from both engines. But it stops when the engines are shut down and I never see it in warmer weather. I was told it's pretty normal.

I to have experienced this with cold temperatures with my MAN 820s. I was told not to worry about it. I will say I don’t believe I ever saw the same amount of “sheening” as the OP’s pictures show.

I have twin crusader (Gas) motors and am having the same issue when I turn it off. Fluids are up and proper. Last trip we traveled about 30 Nautical miles and I noticed it when we docked. Any ideas?

Thank you. It does have carburetor. And yes I had a pretty good starboard breeze that day. Had a hell of a time. Docking. I will have a look at fluid level in the transmissions as well