Clown picking on goby agter many years? Now what?

Hi, I have a 40 breeder mixed reef that has been established for at least 5 years. I have 2 oscellaris clowns, a yellow watchman goby and added a sixline wrasse 3 weeks ago. I left on vacation and my goby was looking a bit thin. Now that I'm back he looks beat up. I'm now noticing the clown picking on him multiple times just in a few minutes. The new wrasse doesn't seem interested in him at all. I've read clowns can become aggressive. Does it make sense after all these years. I've had a sixline in there previously with no problems as well. It could be possible the goby is just old and getting picked on because he's getting sickly.
Anyway, what should I do? Put the clown in quarantine? Get rid of him?
Thanks