1962 M21 drive side bearing non standard extra part.

[watts]

I have swapped cases because mine were damaged.
I was curious to push out drive side bearings as it appeared to have an extra bit.

It is now out and it has two extra bits one a very fine washer and 'bush' which was pressed into the case. It always struck me as odd because it turned in the cases.  I suspect a diy job but to what purpose?

Has anyone seen this before?

Thanks

Matthew