Neighbour having trouble locking his door. Key does not turn smoothly and sometimes sticks completely (whether door is open or closed). Removed Euro cylinder which tested ok with key turning smoothly each way. Now thinking it may be the internal gearbox at fault as handles seem very floppy and latch does not spring out fully as though spring is knackered. To remove gearbox, do I completely remove the metal strip that runs from the bottom to the top of the door's front edge? It seems to be secured by self tappers. Does the gearbox come out attached to this strip? Are there any pitfalls such as loose parts falling about when I remove it from the door? I would appreciate some input. Thanks.