I replaced the glow plugs today (done as suggested) & fitted the new rail, it was actually Plug 1 that was corroded that had the wire also connected, it had mild corrosion so I filed both sides down to new metal, I found 2 plugs (2&4) had the base broken off them & plug 1 was completely black, put it all back together with a new intercooler & it kicked over in 2 seconds & idled smooth as, noticable increase in power & response was much better, no smoke or strong diesel fumes on start up, will kick it over in the morning to confirm all is back to normal, fingers crossed