I have an FWB80 which was serviced about 5 years ago. I've not shot it for about 3 years and when trying it today the recoilless sledge mechanism doesn't appear to be working and the pistol is recoiling. When working correctly the sledge should recoil/move fully to the rear then if you tilt the pistol downward the sledge should slide forward and lock. This doesn't happen, there is no movement of the sledge at all. Even when it was working it did occasionally stick but it's not working at all now.

Could it just be lack of use? Any suggestions?