Those bushings in the trailing arms are shit, end of story. I'm very much not surprised they're coming apart on you.
The trailing arm replacements don't come as part of the ES master set 'cause they're rather expensive. Personally, I'd pick up the ES master and then the Prothane units for the trailing arms. The Prothanes come with upgraded metal bits so you don't have to clean & re-use the OEM metal.