Lee, that is the original buttplate, they tend to sometimes show a slight separation after 60 years or so. someone has done a bit of scrubbing one the lock plates, it may have had some flash rust at some point. This is the type of gun that I would have re-casehardened by a pro and then I would refinish the stock myself.
I imagine this one will bring over $750.00 easy enough, even in it's not so perfect condition. These nicer old L. C.'s are geeting hard to come by now.
Dave