Ducati have helped out some on here with bikes well out of warranty, if you have a good working relationship with a dealer they might well help you as well. Personally I would have tried that route first before attempting repair, give Ducati a chance to see for themselves what has happened.
The rads on these bikes are curved and ally, most car stuff is a lot cheaper, flat, and on older stuff easier to repair.
If ya dont' get anywhere and need to a new rad it might be worth joining up to get ya 10% off
Ray.