I found this weird spring on the C# key. The original spring is broken flush with the post and stuck. Although it would usually be easier to remove it and put a new spring, I guess whoever did it could make this spring but not remove the old one. It's actually very smart and accurate to fit exactly.
Maybe a bit hard to see in the photo, the springs uses the key hinge as a pivot, wraps around the C# key post for support and hooks on the C# lever linkage rod.
Maybe a bit hard to see in the photo, the springs uses the key hinge as a pivot, wraps around the C# key post for support and hooks on the C# lever linkage rod.