Hi,
My early 07 +4 had a metal radiator when I bought it in May this year. I found that the solder between the lower tube plate and the bottom tank was pourous and therefore leaking. I changed the rad for an alloy one from Mulfab ( there are other suppliers) nice piece of kit but not cheap. No more leaks now.
Not what you wanted to hear I know but it seems this is quite a common problem.
Cheers
John
