I have a display (de-activated) No. 4. After about a year's neglect, I took it down to oil it & found the action very jerky. I could open the bolt, close it (with a very strong final push) & fire off the action. I then removed the bolt, examined it (seems OK) & replaced it. Now it appears jammed in the closed position. It's a US version, with a small piece at the top that you detach from its guide to remove the whole bolt. The bolt handle rotates very smoothly from open to closed, but the piece with the ejector hook does not release & the bolt will not travel to the rear, so the action does not cock & cannot be fired off. Given that I have probably not described the working parts correctly, does anyone recognise the symptoms or know a remedy?