from what i remember, that ring was used for "heavy duty/taxi"
service, and i have seen those on every thing, but not necessarily as intended. there doesn't seem to be any rhyme nor reason as to where these things pop up. i have seen these on all body styles and all engine/trans combos, but they are not on all control arms. in the past, i have fabbed those for a couple thou press fit, and installed them on both bushings. they are not retainers, but are used for extra support. i really don't know if it was worth the effort as i wasn't into any handling improvements at the time. it couldn't hurt. i also don't know if they are available re-popped. any one else with more info on these rings ?