Anything between the mute switch bracket and outer button?

I'm replacing the back cover to a 3gs.

I'm having a lot of trouble for what concerns the silent switch; I have bought these three parts on ebay:

- mute-power-volume-headphone jack cable

- outer switch

- silent switch bracket

I figured out that I had to glue the flex to the bracket since the provided adhesive is definitely not enough

Anyway, there is too much play between the back cover and the outer switch so that it works but it doesn't stay in a stable position

I recall a small piece of rubber being between the two original pieces, could that be an essential part and the reason it's not working as it should?