I myself would have taken the stock off and gave the internal guts a good cleaning. I've repaired a CZ that my buddy from the gun club owns. His problem was the barrell lug that the forearm clips into became un soldered. I sought advice from the 88 year old gunsmith from down the street and I silver soldered it back together, it's worked flawlessly for three years now. He worked on guns 50 plus years and repaired a ton of cz shotguns for the local shop that sold them. His opinion was they arent well put together. He worked on some that had cut off nails for pins in the trigger assembly area. I have a cz o/u 410. It works fine and has about 7k rounds through it. My buddies had 12 through it when his failed,he also had a 28 guage that failed for major repair at 9k rounds. My browning 20 is my go to shooter, I have about 500k through it without a bobbe of anykind. I've seen a couple of kids at the club have trouble with their CZ O/u only when it rains,that tells me the wood is swelling in the trigger area and causing just a bit of drag on the spring . A mirouko is the same as a browning.
