ah fair enough, you want this one then if its a 1.8 rad:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270710843296unless you can fix it by faffing with the blanked off nipple

have a close look at it mine looked like it was coming from there but it was actually coming from the end cap at the top. i have also seen the plastic caps get split by a rusted up upper rad carrier bracket where it had swollen up with rust