But a new radiator and that's it. All radiators have plastic necks.
Unless you ask a radiator shop to make the plastic tank and the connection in aluminium like my freind in Japan did. But the price for that was the same like a complete new radiator
http://www.bimmerboard.com/forums/posts/107961
And even that was not bullet-proof, recently the plastic Y-piece broke, now he has a stell Y-piece
http://www.bimmerboard.com/forums/posts/237442/
A new radiator is not that expensive.
Of course a radiator can be made completely of aluminium, but look at the prices Zionsville is asking for that. For that price I can buy 3 standard ones which last the next 20 years.