I have the same problem shown in an older post here regarding
a paint defect on the top tube around the rear cable bracket.
Apparently Trek Support is not what it used to be. I was told by customer service that this is considered normal wear, a result of sweat, and I will need to pay for a paint job, or I can sand away the finish and remove all the corrosion myself!
This is a 2001 model, but is wiped down after each ride and kept spotless during the winter months.
The lesson here is don't buy a Trek if you sweat a lot?