Oil Leak

[c4keislie]

Hi guys, new to the forums (although I have perused various topics on here before). Having an issue with a GZ250 that I just sold to a friend (which makes me feel horrible, of course). Here's the deal: My friend was driving the bike and noticed that it was leaking a substantial amount of oil out of the side of the engine. I did a quick image search for a 250 engine and highlighted the area of the bike where the leak is (I may be able to post pics of the actual bike later on if necessary):



Any thoughts on what may be causing this?