The spring is fairly easy to replace in any kind of TX. They are available at some hobby shops and my local hardware store has replacement stock as well. People very often swap out the originals with stronger ones as a preferred modification to their new TXs.

The backs of almost every Futaba I've ever worked on come off easily with the removal of the screws that're obvious on the back of the TX. The springs are usually fairly easy to see and not really hard to replace if you have small needle nose pliers.

The manuals that come with a lot radios mention replacing those centering springs with stronger ones. The mfg's don't usually suggest something like that unless it's fairly simple and easy to do. And it is.