Some games don't always have the correct posts installed, so an "official" rubber kit might not match your particular game.

While kits are an easy purchase, It's usually best to take the time to look at the rubbers in your playfield diagram, look at your actual playfield to see if they match (because of errors, missing rubbers, alternations from mods, and/or differences on your playfield), make a list of what you need, then also order a few extras in case you miscount or unexpectedly break some.

Rubbers are pretty cheap, and there's really only a handful of different sizes.