I was riding down the road on my 2005 harley sportster when it started to miss ,while I started to pull over I felt and heard a pop , I shut it down and after looking it over I found that the oil tank split and the oil was coming out ,what would cause this?

What is the tank made of? If its metal you may want to contact a harley dealer and see if there has been a recall. It sounds like a weld broke loose.

A manufacturer defect.