Part ID Help

[fatsanta92]

I ordered a Di2 Junction Box A, used, from ebay.

All works well with it but it doesn't have the tiny piece of rubber that sits in the curve when it is strapped to the stem via the mounting plate (part ID Y7FE98010). As a result, the box sits just loose enough where it shifts around, and unfortunately cutting off another link of the rubber band makes it too tight to put on.

Does anyone know what this piece is called/where I can acquire one?