Muffler Issue On Engine Model # 10J902 ( 4 HP )

Hi,
I have a Bolens pushmower ( Model # 11A-074D765 Serial # 1B036K31687 ) with a 4 HP Briggs & Stratton Model # 10J902 Type 0342E1 engine on it. My current issue is I noticed the original muffler that came installed on it is loose. I've already purchased a new replacement muffler to install, but I can't get the old one off. It seems as though the muffler is loose on the back side of the muffler, so I can remove it. Also, engine oil is leaking out onto the deck..does anyone in here have any suggestions on how to fix this ?
Thanks,
David

Those pancase muffler will come apart internally, and the outer shell spins on the threads. You will need break the outer part of, so you can get a hold of the threaded part and unscrew it. You will need to clean the oil off and then determine where it is coming from.. Could be the sump gasket, or could be related to the mower being tipped if that is a possibility.