I bought a '99 Trek 5200 new in January 2000. I have about 50,000 miles on it and it's in fine shape, except for one very frustrating thing. My frame has two aluminum cable stops for the rear brake, epoxied to the top tube. No fastenings. These cable stops corrode to powder in 3-4 years. This is not good, to say the least. I understand the mechanism: corrosion of dissimilar materials (carbon and aluminum), far apart in the galvanic series. For them to corrode, they need to be in electrical contact, and subjected to an electrolyte (sweat, dirty water, or just high humidity).
There is another possible mechanism for the corrosion: the cable housings and cable ends interacting with the aluminum. I suppose that's possible, but I don't use anything unusual for cable housings or ends. Right now, my cable housings need replacing and they're corroded into the stops so I can't remove them. I can see that if I pull hard on them at all, the rotten aluminum will crumble.
Anyway, they corrode, and take the surrounding paint with them, now much of the top tube paint is gone. Trek has warrantied the frame twice and it needs it again. I'm without the bike for 2-3 months, and they make me take it to a dealer for disassembly and reassembly or they won't warranty it. And this costs money. They send the frame away, Trek replaces the cable stops, repaints, and returns it. In less than a year's time, I can see the stops begin to corrode again. Trek claims that my frame is the only frame out there that this is happening to. I find that hard to believe. I'm not a particularly heavy sweater, and usually ride fast enough that the sweat does not drip vertically off my nose onto the top tube. My area does not salt the roads, and I only ride this bike in the rain during occasional brevets or if caught out.
So I'd like a little advice before I send the thing off again for another failed "repair."