it's purely vibration absorption, there's no real flex involved (or at least there shouldn't be as it's just a mount for the differential). the most common fix (aside from a random junkyard part that just happens to be a bit better) is to remove the bushing and cast the whole thing in urethane. not as absorbent but works all the same to hold up the diff. the problem I was having with the old is the rubber at the top was crushing so much that the diff was rising up and contacting the engine, causing a bad vibration. come to think of it, this issue may not even happen in the v6 KJs. that would explain why I found it hard to get opinions on what to do.