No damage to mine yet, and I usually leave them cocked. Of course, when I'm feeling really responsible, I pull the bolt back half way and pull the trigger, then let go of the bolt. Solved the problem for me.
Sorry, I forgot about that. If you have a bolt-action, do it like Padre says. If you have a semiauto, do it like I say.padre said:try this
if your Marlin rimfire is cocked.
Pull up on the handle, press trigger pull handle down . Should uncock without firing pin damage.