A bit of further research yields a much better answer. All of that
macro below can be replaced with just one line:

cells.SpecialCells(xlFormulas).Select

The equivalent manually  is:
Make sure no multicell range is selected (that would restrict the
resultant selected cells to within that multicell selection)
Edit dropdown menu|Go to...
Click the Special button
Select Formulas, (leave all checks in place)
Click OK
THEN do your find/replace.