A part of the plastic housing came loose and fell out while biking. The part was lost so gluing it back in wasn't an option. I tried spreading some silicon caulking around the lock mechanism to keep it in place within the housing but it didn't work well. Sugru seemed an ideal solution for this.
Step 1: Clean the Surfaces and Tape Up the Lock
Remove any dirt from the lock. In my case I had to get rid of all the remaining silicon caulking from my previous attempt at fixing the lock. Cut a piece of tape to place over the keyhole to make sure you don't get any Sugru inside.
Step 2: Apply the Sugru
I used an entire mini-pack of black Sugru for this. Your lock size and colour will dictate what you use.
Knead the Sugru with your fingers and form it to the size and shape you need. I kept a small amount of the Sugru separate in case I needed to patch up any holes around the edges. By matching up the size/shape as best you can at the beginning you can avoid cracks/lines where two pieces of Sugru meet.
Work the Sugru into the space with your fingers. Use the leftover Sugru to fill any holes as needed. You can remove most cracks and fingerprints by wetting your finger slightly and rubbing it over the Sugru until smooth.
Step 3: Let the Sugru Harden
As stated in the instructions, the working time for the Sugru is 30 minutes. Make sure you are careful with your work while it hardens. I wanted to remove some of the shine from the Sugru to match the rest of the plastic on my lock. I found that rubbing the Sugru with my finger at the 30 minute point took some of the shine off it.
Set your lock aside for 24 hours to give the Sugru complete time to cure. Remove the tape and you're good to go.