had a kangoo a few years ago with the same problem,pump,injectors,fuel lines and tank clean were all done under warranty,whether this is a problem for renaults,you would have to ask renault but dont think they will own up to anything,have heard of magnets being put at bottom of filter element as you say but that is what the filter is there for and would renew it regularly and a fuel conditioner every now and then wouldnt do no harm,if you have done all this work dont think there is much more you can do but hope for the best or once fixed and running ok punt the motor on and dont buy a renault,have you seen the number of faults on here relating to electrical problems on renaults?
cdc, November 2010