Ok, carcass removed - how to open top plate?

I have removed the draw carcass of my Zanussi FL828 (a bit of a pain, obviously the guys at Zanussi did not design it with ease of maintenance in mind). Thanks for your help CK. I now see that the blocked pipework is encased in the top plate; the pipework is formed by two layers of plastic (polystyrene?) glued together. I have flushed water through the pipes and, on the assumption that the clogging is 'fur' (calcium salts from the water), I have immersed the top plate in vinegar. Any other ideas of what I could do? Should I break the two pieces of plastic apart, if so how can I do it with minimal damage? And what glue should I use to reassemble?