They did not resolve it, unfortunately. Not for existing frames anyway.
I believe the problem arose because they bonded the aluminium dropouts to the carbon without using anything in between, which supposedly is a perfect basis for galvanic corrosion. Although corrosion on aluminium itself is not something you should worry about (it stops as soon as the entire surface is corroded), the problem is that the corroded surface is bigger compared to non-corroded aluminium. As a result of this the carbon will crack ones the corrosion becomes bad enough.
That Colnago did not resolve it makes no sense to me. Current C59's have aluminum dropouts in the forks. Other bikes as well. We're talking almost 20 years later since the first C40's. To say they haven't resolved it for existing frames seems strange, especially since you seem to imply the problem arose from bonding the aluminum dropouts to carbon without using anything in between. If you know that, I'm sure Colnago does too, and if they didn't back then I'm sure they do now. How are current aluminium shelled bottom brackets bonded to carbon these days, not just with Colnagos, but any frame? The same issue should result there right? What is it that goes between the aluminum and carbon to bond it so that it doesn't corrode. I don't believe there is any problem with corrosion on current frames, so I would say if this was a known issue it was in fact resolved long ago, but I'm guessing. For history's sake and furthering my own knowledge I certainly would like to know more about the fabled C40 bonding failures as I have friends with C40s. Also, I used to have a C40 HP B-stay and never noticed anything amiss with it. I sold it when I ventured into C50 land and still haven't had a single problem along these lines.
I consider myself fairly knowledgeable about Colnagos and their construction, but this is an area I really don't know much about but would like to learn what the real story is once and for all. So if anybody has more info I would love to hear it, maybe via PM so as not to further hijack @Ozrider's thread any further.
@Ozrider: If possible could you perhaps post a closeup photo of the dropout area? It does look corroded in the photo, but maybe a sanding down through the oxidized layer and coating it with some protectant might help stop any further corrosion. Looking forward to the build.