When you degreased the engine, did you scrub it down every place that looked oily?
There is a rubber boot over the differential on the back of the engine.
I thought my 650 was leaking out of the engine where the drive shaft exits the case. It was actually the rear tappet cover all the way up on the head. I had adjusted the valve clearance and did not replace the o ring on the tappet cover. The oil started oozing out slowing, all the way down the side of the cylinders to the case, spreading out everywhere, and then dripping a bit down by the drive shaft.
I thought it was the drive shaft seal flinging oil around while it was spinning, until I soaped the whole back of the engine down with laundry soap. Then when I started it up I could see the oil oozing out all the way up on the tappet cover on the head.
If you have cleaned everything good, dont assume its coming from one place or the other until you can see new oil coming out at only one place.
The other thing I would suggest is to make sure you did not overfill your crankcase. Sit on the bike with a small mirror in your left hand and reach down and look at the site-glass window, holding the front brake with your right hand. you can lean the bike a bit left and right - if you cant see the oil line in the top of the window, even when you lean the bike to the right, your case is overfilled. That can cause oil to be forced out of seals that normally would not weep while the bike is running.
If you are sure its the rear drive shaft seal, you can find the Vstar 650 factory Service Manual online as a PDF download, from a couple websites for free. There is a section there on replacing that shaft seal. I have never heard of anyone needing to replace it, so I dont know how much work it would be.