Learned something new today. Didn't know that people retouched darkroom prints with paint brushes. Nice to know that that's an option.
Some more nomenclature

.
Spotting isn't really well described as "re-touching" - at least not the simple spotting needed for dealing with dust on the negative at the printing (or scanning) stage.
"Retouching" better describes a process one employs to essentially edit the contents of a negative, or in some cases a print.
For example, if you have dust on the film when it is in the camera, there will be a blank area on the film - you re-touch to deal with that blank area when you create the final result.
Traditionally, and in certain circumstances, talented Re-touchers would actually work on the negative itself, to remove details, or sometimes even add them.
For example, the classic formal portrait of the family, where uncle Henry miraculously gained back the half of his right ear that he lost in the war

.
And as for the "paint brushes", think instead of "spotting brushes". They are designed to place the smallest possible spot of fluid on the print.
When you spot a print, you don't paint in the spot. You build up the tone with lots of tiny little stippled dots, laid down in a slightly random pattern within the area needed to be spotted. A really good magnifier is important!
I actually use a substitute for the spotting brush - a set of very fine point pens called Spot Pens. They are pre-filled with various tones of spotting fluid. They aren't made any more, and no you can't have mine!