Always replace together. People can tell you whatever you want but you need to replace both of them especially at that mileage. Never replace suspension or steering components as a single. I have never replaced just one that’s crazy. The only time I did was when one side was faulty on a customers car and Subaru replaced it under warranty but the car had under 10,000 on it which I still didn’t want to replace just one. From your picture it looks like it’s just the end link boot busted that’s leaking grease. So I’d replace both of those and see if you continue to see this issue.