I have had most of these brushes for over 5 years.. I use both acrylic, and enamel paints with these same brushes.
I clean them by first wiping the excess paint off on my rag, then rolling them gently against the inside of a glass of the appropriate thinner.
Never bounce the point of the brush off the bottom of the glass ! Then just wipe off on a paint rag or paper towel.. that's it, no extra rolling or trying to get inside the bristles.
If the brush starts to build up too much (from lazy cleaning or old thick paint) I give it a quick clean in lacquer thinner, fixes it right up. Beware of mixing polyester bristle brushes lacquer thinner, the bristles will curl and sometimes fall out of the brush ferule... ?
One thing that may help in not letting the brushes build up too much paint, would be to dip the brush into the appropriate thinner before dipping in the paint.
This helps in the flow of the paint as well.
Happy Building
Cheers