Changed the oil and started my 03 wr450 today and did a test ride when smoke started pouring out. Oil is basically pouring out from a hole in the cylinder head right above the exhaust pipe. I went and checked my buddys bike and he has a plug inserted in this hole. Almost seems like a freeze plug or something. Its about 3/4 inch plug that goes into the cylinder head about 2 inches above where the exhaust pipe goes into the head. What is this plug, where do i get one, and what would case this to pop out. Thanks in advance.