Get a new linkage kit, and check your gear oil before panicking. Just replaced my engine, and car has been off the road with the gearbox in my shed for about 2 months. Gearbox was fine before, but now it keeps popping out too. I have replaced with new linkage kit, and am renew my gear oil. Whist in the shed, it tipped over and a little spilt out, I'm hoping this will solve it. Would suggest doing the same before forking out on a new gearbox.