iPhone 3GS Outer mute switch loose and erratic

Hi everyone and in advance thanks for reading further, if you do that is.

I recently undertook my biggest iPhone repair, replacing amongst other things the headphone ribbon cable on my 3GS and now have a bit of a problem.

Once everything was back together the outer mute switch was very loose and not actually attached to the inner switch, vibrate would switch on and off every time I touched the phone.

Some online advice suggests there is a foam pad of some sort between the two, but I don't appear to have this, my questions are:

Is this foam pad necessary, or in-fact does it exist at all?

There are two indentations on the back of the outer switch which of these does the inner switch fit into, the deep one or the shallow one next to it?

Thanks again for any suggestions.

John