Previous head work was not done correctly, and the chain guide for the cam chain was mis-routed, causing the cam chain to grind away on the retainer bolt.
Best course of action is to replace the bolt, and check cam chain for excess wear. If that is the original cam chain, it's likely to be well past EOM stretch limit.
I had to fix one like that for a KLR bud. See pic below with guide (shoe) outside of socket.
Not sure about the sliver, but it does resemble a circlip - typically used to retain the balancer sprockets.
Highly recommend a very thorough inspection of those internals to ferret out any other gremlins from the PO.