I lament Trek no longer making the 520 disc, especially well equipped from the factory with those front and rear racks, I think about $1500 IIRC. I saw one locally and was impressed. Masi also had a good tour bike same year. Both gone now.

I'm surprised the seat tube broke there, that is more common on folders with hugely long seatposts for much greater bending moment (happened to me), plus the Trek was steel, so better fatigue life. Sloping top tube doesn't help dagnabit, a level top tube would mean a shorter seatpost.

Touring cargo load had zero to do with that failure. However, it may have to do with the welds being left raw, so a stress concentration right at the edge of the (convex) weld; Cannondale would post-dress their welds concave with a strip sander, and with an aluminum frame that was more critical. I have 70k miles on a racer of theirs (with level top tube) before switching to a folder for townie use.