the great Brian Baylis used to say that replacement of the DS dropout was the most common repair he performed. He believed that running an oversized axle (where a 126mm axle was just "forced" into a frame with 120mm spacing) was the proximate cause.

The bending moment applied when the skewer was tightened would cause fatigue and ultimately failure of the DO, because of the forces applied at that brazed joint over 1000s of pedal strokes.

so moral of the story - don't just "force it in there". Cold set and re-align the drop out faces.

/markp