Yeah, and the darn plug probably still oozes oil. I know every bike I owned did.

 

my 2014 does too. Never loosens, just doesn't seal effectively. It's not going to affect anything, no need to top off, but still shouldn't do it.

 

I find that funny - shouldn't do it. Reminds me of a hydraulics manufacturer who was commissioned by a hospital to make a gurney with hydraulic drive wheels. He made them and the hospital complained because they seeped hydraulic fluid. His response was - "they're hydraulic! Hydraulic leaks!"

Point being oil is such a small molecule it is easy for it to seep through the smallest of spaces. The reason why car motors and transmissions, as well as differentials will have oily coatings - it seeps out and spreads in a thin layer over a broad area. So as much as I hate to say it, the manufacturer does their best to have those caps not leak, but they still can and will in most cases. It is nature of the beast.

 

No one is saying it should leak a different type of fluid, we're saying it shouldn't leak, any fluid. My Honda doesn't, my Moto Guzzi doesn't; hell, my Harley didn't.

 

What I am telling you oil is thin and your oil plug doesn't have a complete perfect seal. It can and will get past an O-ring seal or gasket unless everything is perfect. Look under the hood of most cars, they aren't supposed to leak either. No engineer designed an engine, transmission, or differential to leak, but they do. That was the root of comment from the hydraulics plant owner. They're hydraulic and they leak, nature of the beast. They aren't a leak of any volume. It is simply that oil can squeeze through small places water can't get through and spread around, looking like a major leak.. One of the reasons Mobil among others, won't usually recommend using full synthetics on old high mileage cars - oil leaks will suddenly appear. That is what we were told when using Mobil1 in our motorcycles. Smaller slipperier molecules get through smaller places. That is what I am pointing out.

If you can keep oil far enough from the filler it won't leak, like the tank on a Harley, but if enough oil gets to the area the odds are in favor of a bit of oil coming out. The 250 filler is in the area of the primary gears and will get a fairly constant spray. A lot of people never notice the slight oozing if they clean their bikes often enough. I've run into problems trying to seal bolts that simply have oil lay on top of them while the same seal will not seep oil when it doesn't lay on it.

Consider yourself lucky, the gear case on my Guzzi seeped 80-90W gear lube and Hondas still oozed a bit of oil from the fillers,. If the seal isn't perfect and there is enough oil splashed around it will have some ooze and oil spreads. A few drops will spread out over a wide area.

Try getting a new O-ring, the old one may have shrunk. You might be able to try a slightly larger SAE size if possible. If you really want to seal it try smearing some non hardening Kawabond on it. Any bit of crud may cause the tiniest gap in the O-ring seal and oil will seep.