Is the bajonet purely mechanical or electrical as well?

Yes! Your lens mount is both mechanical and electrical. The auto focus and diaphragm control is through these contacts as well as the needed power to move the servos.

The contact block contact is more than a spring its also a contact pin which can get pulled out of the block when they get stuck, so the black plastic block is also damaged.

This will require a new contact block and will need a fair amount of disassembly and you still need to get the part. Best to get your camera to a local camera repair expert or Canon directly.

Your update points to the tensioning leaf springs within the mount. This forces the lens to be indexed against flange face so its alignment to the sensor surface are parallel and at the correct depth.

This part is needed and you can replace it (mechanical). You will need to remove the mount to gain access to the screws which hold the spring.

Do be careful as you might find some spacers under it make sure you put them back in the correct placement. If you get a new mount assembly transfer the spring not the mount!