Aido
That is truly superb - everything I need to know is in that link - thanks so much! I've been back to National Tyres and had it up on the ramps - the chap I know put a bit of welding filler in for me & suggested I go to a local specialist exhaust maunfacturer as the boxes are all fine its really just the two pipes running throught the centre section to the back boxes that have given up so there's a chance I just need a couple of bespoke pipes made up which can be welded in situ onto the boxes. Fingers crossed, but at least I know what to do if I need a replacement as I've been able to identify the section as 17420 from your diagram link.
Thanks again bud....
Ian