This is a re-post of what I wrote on SpeakEV a few days back.
The battery in my key card had failed. Note that in the “non-keyless” version, the car does not warn you about that. I removed the mechanical key from the key card and put it in the lock. Turning it, the ring arch, acting as a lever snapped off. You can still see the original crack in the picture below. The arch is made from a hard rubbery material and it had obviously weakened over time. Glue was no option. The material is not very suited for it and anyway the levered forces on that tiny surface area would be way too high.
What I decided to do is first glue it with super glue to ensure it’s original shape. Then I used pieces of small black nylon tie rib to reinforce the arch. Using a hairdryer I bent one piece to follow the inside curve (where the key ring pulls), then glued it in with two component resin. I repeated that for the (flat) bottom part, filling up as much cavity space where I could. For extra strength I also put a third strip over the slightly curved top of the arch, diverting even more force from the original crack. I let it harden and then used a power file to grind away excess resin and sharp ends of the strips. Finally, I touched it up with some black permanent marker. I expect the nylon to last forever, the metal key ring will not shave that off soon.
Bottom line is: when using the mechanical key, tread very lightly. Also, do check the integrity of the arch part of your card. If in doubt, you might want to do something about it. I did with SWMBO’s key.