Selection.Replace replaces in entire workbook despite Range.Select

I am trying to remove the last character in a text string (for a specific range, on a single worksheet) using a macro and it ends up intermittantly removing that character throughout the whole workbook.



Here is my macro code:

Range("$G$5:$G$19").Select
Selection.Replace What:="Z", Replacement:="", LookAt:=xlPart, _
     SearchOrder:=xlByRows, MatchCase:=True, SearchFormat:=False, _
     ReplaceFormat:=False

Here is an example of my data:

12/22/2011 14:23:46Z
12/22/2011 14:45:12Z
12/22/2011 16:43:46Z
...

And I want to make it look like:

12/22/2011 14:23:46
12/22/2011 14:45:12
12/22/2011 16:43:46
...


On some occasions, Not everytime, the macro will end up removing the "Z" from the entire workbook, instead of just in the cell range G5:G19.

I am running the Macro by clicking on a "Button" on the worksheet. I have about 45 worksheets in the workbook and all of them have this button on each worksheet.

Thanks for the help!