Finding an oil leak. '85 CB750SC Nighthawk

[Kiereek]

I've had a slight oil leak for a while. I'm just trying to figure out where it's coming from. I've cleaned off the area and taken some pictures.

My first guess was that the o'ring on the drive shaft holder had gone, but now I'm not so sure. Today while cleaning the area off, I noticed this weird area that looks like the metal has split. It seems like it would be a hell of a leak if this were the culprit.

Could someone please confirm whether this is supposed to be like this or not? I haven't had the bike that long, but I feel like I would have noticed this before now.

Here's the album with some pictures. Any thoughts are welcome.
http://imgur.com/a/8eEUK

 

[amc49]

You need to mark the exact location of your weirdness............beyond that I see some casting worm there, Honda cases are full of it and harmless.

 

[Kiereek]

If it's just a casting vein, that would be great. You were looking at the right thing there. Most likely it's coming from behind that rubber boot then. I'll report back when I know for sure.