How much oil is in the airbox, have yoe opened the drain? How much oil did you put in? how did you check it? You are going to have to find the source, I can't do it for you? Is filter on correctly?

 

I'm with you here.

 

Sounds like you have a gas leak. The gas leaks from the petcock or whereever, finds its way into the case and ups the volume of fluid in the case. I would find or rule out a gas leak before running it again, the change the oil. Gas/Oil is a killer of older bikes, but if caught in time you should be fine. Best of luck.

 

Where do you get gas leak from. OP doesn't mention Gas smell or anything. Besides Shadows are pump fed. Fuel leaks go on the ground not the motor, like a gravity fed system. Fuel smell is more a sign of bad AF Mixture, miss-adjusted floats or weak rings.

 

hmm old o ring from old filter got stuck on ? missing o ring ? get some pix could help to see

 

If I read you correctly, it started leaking after you changed the oil? If so, it's pretty obvious--filter probably isn't seated right.
If I don't read you correctly, it's still most likely a simple fix.
First, take a photo and post the pic.
Second, remove the filter, clean it all up, reinstall it, and run it again.
Check here again after you've done that.
As a general rule, especially since you're new to bikes, start with the simple stuff and rule it out first. Most times, you will get lucky and find it fast. You've got a good, reliable machine.
One step and a time. You do more than one thing at a time, and you can't be sure what makes a difference.

 

I'd say you might have the old filter seal stuck on with the new filter. This has been happening alot lately on my other vehicles but it's a part of inspection process while changing oil. I use Supertech filters most of the time.

 

Could definitely be from that old seal. I've done that on the Mother-In-Law's Ford Escape and it scared the crap outta me when I started it - the oil went everywhere. Sure enough, the seal was stuck to the motor. Always check the old filter...
If you can't figure out where the oil came from, clean up the wet area and put some baby powder there, then run it. In a short time you should be able to identify the source of the leak.