Weird metal piece included with the new truetrac diff

Hello i realise this is an old thread but the trust spacer or slug for the truetrac do you know how it is inserted i'm hoping you are able to go through the axle tube as i;ve just realised that mine also is missing and hoping i'm able to remove one axle and slid it in with out going through and pulling the diff down again
Magnet and a curtain rod will work. Attach magnet to rod. Stuff it in and slide the magnet off.

Or, put a dollip of rtv on the end of the axle, stick spacer button to axle, let dry, insert into axle tube.