Looks like the joint cracked off just above the exhaust outlet.. The thing has a left handed thread on one end and a right handed thread on the other (I don't remember which is which) so it is not common. The Yanmar part number is 104214-13580, and costs about $40. Best to get an outlet gasket (part # 128370-13201about$8) and pull the outlet to get at the part that is stuck in the threads.. Good Luck