Sounds so much like an issue I had with mine when it was new. Yet the situation is different.
I bought my '07 Stratoliner and immediately loved it.
Soon there after I started seeing traces of oil blowing back on the bags and sides of the bike but never a puddle or a drop on the ground. But it was clear it was coming from the rear cylinder head area. Since it was under warranty, I took it into the dealer. They said it was the rocker cover and had the bike 3 days replacing it. Again the same results of oil misting back. I returned it again. They again replaced the rocker cover/box gaskets, and another week riding lost. Within 2 days it was more than clear the issue remained.
Upon return to the dealer I went up the Management ladder. The entire head was removed and inspected. I was called in to review the situation. They could not find a reason for the leak. I saw on the machined surfaces for where gaskets made contact, something that did not look right. I could clearly see grinding marks that resembled a rough cut board. The grinding marks looked as if it was hit being ground clockwise, then counterclockwise. Although it looked like course cutting, it was very smooth as glass. With a straight edge, you could not see light in grooves or uneven cutting. Yet it looked horrible.
Although the straight edge showed it was all true, and no imperfections felt, I was able to show the Management that it just did not look right. Not wanting to risk a very unhappy new bike owner, the immediately sent away for a new head. On it's arrival a quick visual inspection showed an entirely different looking machined surface that looked correct. The head was replaced and I have never again experienced a problem. In fact, that is the only problem I have had with the bike.
Now I am sorry to present the worst case scenario to you that I went thru. Not likely is it your problem as it should have shown itself a long time ago.
It appears old fashion trouble shooting is your course now. Replace and replace until the bad gasket/seal is found or the issue is seen. I hate that.
Keep pluggin away. The bike is a great machine and will again be fun after resolution is found.
Close inspection of all little details will win out.