Just to put things in perspective, and no I wouldn't put Robin's head in an ultrasonic cleaner but my dad was a painter and the best brushes you could buy were boar bristle brushes. They were used to apply oil based paints for decades and then water based and they were cleaned with turpentine and benzine and then soap and water and then wrapped in newspaper and you know what? My dad is gone but I still have those brushes after all those decades. They be as good as the day they were purchased back in the 1940s and 50s...maybe older.

They be tougher than you think.