good luck with the install. i know you will love the J&M arms. J&M does offer great parts & customer service, that is why i have been talking them up for so long.
Just so you don't feel alone - the EXACT same thing happened to my BMR LCAs. I heard a strange "creaking" sound from the rear end and when I checked it out, sure enough, the bushings had split just like yours. Much like you, I didn't want to bother with the same arms again, so I ended up putting on a set of Steeda LCAs and couldn't be happier. I also put on a Steeda UCA at the same time, which btw was a PIA install..
Yeah I'm really hoping nothing happens to the UCA, because I REALLY don't ever want to install one of those again. But the UCA was bought many months after the LCA's, so I'm hoping the bushings are better.