Jon very kindly made this script on this thread. It seems that it'll be useful to more people so I thought I'd repost it here with a more general name.
The script is also explained on the DearOpus scripts page.
The usage is
This will open the specified path. If it already exists in an open tab, on either side of a dual lister, that tab will be recycled and focused. It's similar to the findexisting argument, but it searches both sides of a dual lister.
Please anyone feel free to publish other versions, I just wanted to make a thread for the script.
GoExisting.js.txt (5.75 KB)