Yamaha yz125 wierd leakage

I recently bought a 1989 yz125 yamaha dirt bike from a guy and it runs perfectly. But there is one problem, there is a wierd leak on the right side od the bike and oil splatters on the lower part of my leg, and all over the right side of the bike on the plastic and stuff i dont know where its coming from or why its doing it plz help me!

ya i think that my bike has been running really rich and that oil is blowing from a seal in the exhaust pipe. thanks for the advise!