Cut you a little piece of plastic, just wide enough as servo itself...
Length don't matter, but try to keep it about 1 inch long...
Lay it over the edge of a table with half of it hanging off....gently put some heat to it...
Bend it to 90 degrees, now lay it onto the side of the servo with just a drop of JB weld on the
bottom, pushing it butt up against the broken tab.
Now lay a thin coat of JB weld over it/covering the edges of the
Piece all the way up to an around that and the broken tab
Let dry a day, then drill your holes for servo screws....
I can post a pic of the servo I did if that'll help
explain it better...