Multi-point lock replacement

backboiler

I have a 5-point (I think) lock on the uPVC front door. It's the kind with latch and deadbolt with four rollers along the height of the door. It looks like this http://www.locks.ie/images/products/PAY176.jpg. It's the verson with 92 mm from handle to keyhole centres and 35 mm from door edge to centre of the keyhole.


This morning when I tried to open it the handle didn't turn the latch mechanism (the key for the deadbolt works fine). The handle just turns in circles. I opened it up and see that the circular metal block with the square hole (is it called a cam?) that the handle shaft goes through has split into pieces. The "circular metal block" is the brass-coloured part of the lock shown in the top-right of the image above.

I took out the lock barrel and removed the whole assembly off the door. It's about 1.7 m long and looks like the top and bottom have been cut to shorten it to that length. (Referring again to the image linked above, it seems to suggest that the overall length can be up to 2.285 m.) It doesn't seem to be possible to open the lock mechanism without prying it apart; I see no screws in that part.

The lads in Chadwicks and Brooks looked mystified with the contraption when I brought it in. I see that site (http://www.locks.ie) sells them but I'm wondering how much of the lock do I need to replace? Can the lock part (i.e. just the bit that moves the latch) be replaced and just bolted onto the 4-roller section? They seem to be attached using a 6-sided version of the philips-head screw.