Hi Jakki, you still not sorted this?
after our conversation a while ago i would have said the rad....could u borrow some1's??????
got a gut feeling about this...when i had mine rebuilt i had exactly the same problem... (as i said in our conversation) i had a fairly new rad so was quite concerned something serious was wrong when i had the same problem u are decribing... Luckily my friends 4b4 saff was off the road so i borrowed his rad for the afternoon...installed in and bled the system and volia problem sovled.
But as u say u don't wasnt spend some wedge on a rad when it's not the problem..hense me asking if u have a friend who can help you out
good luck
P.s yes that was a tanned me with the glasses on sunday