Which Octocoupler? (Electronics/PCB)

[Xad]

I'm looking to get a replacement for this:


I've found Optocouplers here but not sure which one to get: CPC Link How do i know which to get? They seem so similar.





Below is what the damaged one looks like. Any idea what causes this? If i replace it is it likely to burn out again because the problem is possibly something else?