Should I replace just the one that is bad, or do the right side too? My dealer confirmed the left one was bad which causes clunking.

 

I'd be inclined to replace both. They've both been through the same treatment. Maybe one hit a few bumps harder than the other. But they're only seperated by like...4 feet.

You'll need an alignment after replacing a UCA.

 

I had a bad upper passenger control arm. It wasn't clunking; but, I couldn't get the it into alignment specs. Replaced just that one with OEM replacement and still couldn't get it into alignment specs. Just went with Heel toe ultimate front/rear adjustable camber set and back in alignment green. My rear camber was slowly getting more out of specs anyways with +100K on the A-spec suspension. I was able to fix both problems with the camber kit.