Guy hands me a Sucrets box of bail parts he took apart and couldn't get back together.
Any idea where this washer goes?
Well a Sucrets box is smaller than a shoebox, so that's a positive. Looking at the schematic, I would think maybe Roller Collar C part (31), or possibly Spool Washer (7) or (8) although your washer looks a bit small for a spool washer.
https://www.reelschematic.com/wp-content/uploads/schematics/Daiwa/Revros/Daiwa%2019%20Revros%20LT%204000-C.pdf
I had an LT4000 through just the other day and IIRC the LR collar was a bit thicker than the shim that seems to be? On saying this, that size looks like it would fit around the post in the bailwire rather than the screw? According to the guys at the Daiwa Aus workshop they get a lot of reels come in with random washers/shims from factory that are not in the schems, although they are usually brass shims or the like. Put the LR together and see what the clearances are like?
Cheers
Steve