The triggers on Dreamcast controllers can be prone to cracking at the point they pivot. This results in the trigger failing to work or trigger correctly. Unfortunately there aren’t any replacement triggers like there are for Xbox or Playstation. However, it is possible to 3D print a replacement part which can be glued to the trigger.

I have a controller that has two broken triggers. You can see in the image below the crack at the top right of the trigger. The other trigger has this part broken off completely. It also looks like someone tried to fix it in the past as there is some old super glue there.

Cracked pivot point inside the Dreamcast trigger.

Looking on Thingiverse I came across a few different models that can be printed, and I decided to use the model designed by sirjeannot . Importing the STL into Cura resulted in a huge model, after a couple attempts I found that scaling it down to 9.5% resulted in the correct size.

Once printed, all that is needed is to trim back the broken tabs if there is any remaining and glue in the 3D printed part with a few drops of super glue.

Broken tabs cut away.
Replacement part glued in place.

Once the glue has dried, and you have ripped off a layer of skin which somehow always happens when working with super glue, then push the trigger back into the trigger frame on the controller PCB. It may take a bit of force. Test it a few times and if it feels like it is working correctly then you can screw the controller back together.

Trigger all fixed.