A crankcase leak will kill a good engine in a heartbeat! Sometimes if the case has a pressure tap. You can do a good smoke test. Fill the case with smoke and watch for it. Look where it's coming from! Very good engine tho. I had a fellow bring one to me. Ot wouldn't run smoothly. Ended up being someone must have stuck a t pin threw to spark plug cable had a severe ignition leak. I wouldn't have found it if I hadn't slid the outer ground back about 2 inches. Fixed it and ran like a top.