How to fix the recoil on a pillar drill lowering arm?

Hi, we have a standard pillar drill and the recoil, where by the lowering handle srprings back into place, rasing the drill head atumoatically after use, has stopped working.

Does anyone have any suggestions as to how to fix this without removing cap to tighten the spring, which will then probably pop out and not want to go back inside the hub?

Thanks in advance for any help anyone can give.

Rupert