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I have a Trek 7200 (Alpha aluminum frame) and it has two water bottle holder mountings, the top braze-on on the seat tube seems to have broken from over-tightening and has sunk into the frame. These braze-ons are recessed into the body of the frame tubes, as if they were somehow attached from the inside.
Is it possible to repair this braze-on? Is it something some super-glue could help with, or am I looking at a permanent wound?
Bosses in aluminum frames are typically rivet nuts, aka "pem nuts", which have a head that should be too large to slip back into the frame.
For your frame, it sounds like the Park Tool directions for securing bosses on carbon frames should work equally well. The top mount on the seat-tube is also the easiest to repair using this method, so you're in luck.
No matter what you do: if you have loose metal parts hanging around inside your tubes, then your first priority is to get them out.
The Park Tools link in the other answer has some good ideas. My first thought would be to get a metal nut or threaded sleeve and epoxy it in place.
But the simplest option is to not fix it at all, and just use a clamp to secure the bottle cage. Your bike shop might have clamps specifically for bottle cages, otherwise use a hose clamp from a hardware or auto parts store.
