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Unfortunately, as I read your question, you're looking to repair completed brushes. If that's the case, the best way to really fix things is to drill out the knot,clean the handle thoroughly, patch with clear resin, and set a new knot; otherwise, anything you use to fill the holes will likely wick into the hair/fibers. One alternative, however might try the following (fair warning, what I'm about to describe is tricky with no guarantees of success, but if you're feeling adventurous and have patience...):
Wrap a piece of paper or (better) blue painter's tape around the knot, getting it snug up against the handle.
Using a soft toothbrush dipped in warm water, carefully remove all traces of soap residue in and around the holes. Once that's done, I would take a que-tip moistened in acetone or rubbing alcohol and go over the the entire area in and around the holes. You want that area as clean as you can get it.
Now you should be ready to start filling the holes. This gets tricky; so go slowly.
First you want to wear rubber exam gloves, otherwise, you could easily glue yourself to the brush(!) (Having a can of Acetone on hand is always a good idea!)
Spray a bit of CA accelerator around the area to be filled and give it a minute to dry.
Then, apply a small drop of medium CA to a toothpick and--with the hole facing UP (perhaps held in a vise)--carefully dab the glue into the largest hole. (Don't worry if it doesn't fill completely the first time around!)
Allow the CA to completely set, then move on to the next hole. Repeat until every hole has been addressed.
At this point, you'll want to examine your work and repeat the process for any holes that haven't been completely filled.
Finally, you might want to wet sand the area to level-out your work. I'd start with 400 grit and progress through the grits (400, 800, 1200, 2,000). Again, go s-l-o-w-l-y. (You might want to use a popsicle stick as a sanding block.)
Finally, you'll want to polish the entire area with some rough cut automotive polish. (This will show any defects in your work; so don't be disappointed if some white specs appear. You can always clean then out with some rubbing alcohol and start over. Just don't use Acetone because Acetone will remove the CA you've laboriously applied previously.)
As I said, there are no guarantees--and there are other ways to affect repairs--but, given what you've written, this might be the best alternative. If it seems too much, I'd just live with the brushes the way they are.