If it has never been apart, the nylon ring may have deteriorated and left the chain to run on the bare aluminum sprocket. Happened to mine. The gear was bare and looked like a circular saw blade when I took it off. Similar symptoms to yours
hopefully the cam sprocket doesn't look like a circular saw blade, hahaha.
I've never done it on a B engine, but you might be able to remove the fuel pump and fuel pump pushrod and snake a borescope in and take a peek.
If it does look like a circular saw blade, all that plastic wiIl end up in the sump, and you'll have to pull the pan and pickup to clean all that debris out.