"You're talking about electrolysis"
Yes, that is right. Interesting that Alfa is insisting on inspections of the joints, as if they don't quite trust what they have done. I'd be leery of driving a 4C in the winter where salt is used on the road, not that I figure that many would take such a chance of driving a 4C on slippery winter roads.
Always a big problem with the new use of Gr/ep composites. The aircraft companies know pretty much how to protect it, though. For example, the 777 horizontal stabilizer is Gr/ep, has been used on that airplane for several decades. Same with some Airbus models.
Luckily, our sailboat is all fiberglass with an outboard motor, so even though the boat sits in saltwater all year, there is no problem with electrolysis. The mildly acid rain does slowly try to dissolve the zincs on the outboard motor, even though it sits kicked up out of the water almost all of the time.
Alfa had the problem of having stainless window trim clips which cut into the painted body metal, thus creating areas of galvanic corrosion in many models. Now, everything is glued on instead.