Replay gain is just a value in the tags, the file itself isn't altered.
You can go to your audio library, select all files (ctrl-a), right click and do library tools->analyze audio.
On 13,000 tracks it's going to take a LONG time. You might want to try it on a subset of your library, like by artist or some such.
Once the file has been analyzed, it will be skipped over if you analyze it a second time.