funny, I just went through this yesterday...greasing up the tractor, 2nd zerk runs out of grease...trip to the HW store, back home load the new cartridge up, press the catch to release the rod, it goes back in easily but no grease pressure...repeat the process a few more times, same thing...the catch tab for the rod falls down inside the tube...entire gun goes in the trash can, new cartridge and all...Tuesday calls for a trip to Harbor Freight or WallyWorld to pick up a new gun...sheesh...FYI, the rest of the day wasn't much smoother!