I've read of damage done by ultrasonic cleaning to bronze parts, such as gears; apparently it can make them much more brittle. But I've not heard of any such damage to brass. It's interesting to see which methods various top repair people use. Read through Dr. Valve's site, and you'll find that your trumpet may receive multiple cleanings in his hands, and he uses both acid and ultrasonic. It might be best to just choose a repair person you trust and let him do what he thinks is best.