My Reel
Using booleans is kind of flakey sometimes. When I make a gear with a hole
in it I use a little different method.
First, I assume you use a circle to make a template for the gear to
extrude. I usually start with a tube (no ends) and scale one end smaller.
Then I scale the lenth of the tube down to nothing to end up with a small
circle inside a bigger circle joined by faces. I modify the outer circle
into a gear template and either leave the inner circle round or put teeth
in it too. Then when you extrude it you get a gear with a hole in it with
the minimum number of points. Since your template has faces between the
inner and outer circles the end faces of the gear also come out OK.