Elgin Grade 387, Is That a Bushing?

You never know what you're doing to find when you get into a watch...  Here's what I found on removing the dial from this one.  At some point in the past a really large piece was cut out of the bottom plate, where the lower balance jewel mounts.  I round piece of brass has been fit there like a sort of giant bushing.  I'm not sure what problem would prompt this...  

Here's the view from the top, after removing the balance wheel.



This movement is a grade 387, 16 size, 17 jewel Elgin, made about 1914.