Cup drive rubber insert?

[Tony Slade]

Hi everyone. I’ve just done my first Diff oil change. I’ve noticed on the rear differential cups only they have a what looks like a rubber insert in them? The cups on the front and centre have Not. Is this a mistake on Arrmas behalf should all the drive cups have a rubber insert in them ?

 

[JvG]

Nope, stock only in the rear cups:

 

[Tony Slade]

Nice One.
Thanks Very Much for that