How to repair/replace my PVC door lock?

My PVC front door lock will not operate from the outside only (looks as though the pins have moved) & the key won't go in. I have assumed that the Euro cylinder needs replacing & have followed some of the advice given for removing the old cylinder. Problem is there isn't a retaining screw evident (even when I remove the protective strip at the door edge & expose the locking mechanisms). Does this mean I will need a new complete mechanism? Or, is there another method? Any advice much appreciated. Not sure of the manufacturer but about 11 years old & put in by a local dealer who is now out of business.