that amount of fuel had to come from the return lines dribbleing down the side of the injector as you removed them. it's wet on top of the injectors. I'd not worry about it. clean it up,and get the nozzels tested.

For something with small volumes - such as an injector - ultrasonic cleaning won't get things clean with out taking stuff apart.

In simple terms ultrasonic cleaners form bubbles on the surfaces of items. The formation of these bubbles and the agitation of these bubbles provides the cleaning effect. It is easier to form bubbles on external surfaces as the acoustic waves (generated in the sonic cleaner) are not always able to penetrate into enclosed cavities.