The Volume Button appeared to have been lost. I wanted to renew it so it would work.
The repair went O.K., but the process was excessive. I realized when I got to the last step that only the top silver strip on the Volume Button had fallen off. In fact, the top silver strip on the new, replacement, Button fell off as I was trying to insert the complete button. I replaced it after I had inserted the thicker bottom portion of the Button. But this could have been done without having taken the entire 3GS apart. All that was needed to be done was to clean the original switch w/o removing it or anything else, and glue the new silver top onto the old bottom. Additionally, I have no significant confidence that the new top will stay on the new bottom because it had very weak glue and does not appear well secured.
So, a better solution for me would have been to have a new top (or even the entire new button from which I could just take the top) and some proper glue to use after cleaning the old button bottom part.
I did learn that I could, indeed, disassemble the 3GS and get it back together. But, separating the silver rim from the back plastic was trecherous -- could have badly broken the rim. And the glue that holds them together is not nicely reusable, so I think the assembly is weaker now.
Since it is next to impossible for the entire Volume Button to come out of the phone -- without major breakage, I think the likely problem of the silver top falling off should have been pointed and simply re-glueing a new one on should have been pointed out.
I did learn how to replace the battery in the process, so I will be ready to do this when the battery goes bad.
Point out that the most likely problem is for the silver top to come off and provide some glue with the replacement button so that the user can simply remove the top and transfer it to the old button bottom.