Blown head gaskets do happen on m112's. The good news for op, since his is NA a used motor is easier and cheaper to source than a m112k. I spun mine from a blown head gasket that got progressive worst. Mine started leaking at 200k and the bearing spun at 242k. Now I didn't care as I was going to swap a v8 in mine anyway. Only reason mine lasted that long was because I was changing the oil like every 2500 miles (my oil changes are free). If you plan to replace the motor you can keep driving it and doing oil changes until it let go, if you plan to have the head gaskets replaced which can be done if you find somebody that knows what they are stop driving. If you spin a bearing the whole motor is trash,

Also if you want to know if its a head gasket, just pull the valve covers, The camshafts and everything will look like the underside of the oil cap. It might be on one side or both.