Whilst admiring my lovely new rear tyre I noticed a large dent in the rim.
The wheel was still very dirty but something else caught my eye. There was a thin line besides one of the adjacent spokes. A closer inspection revealed an 8cm crack that went through two spokes.
After cleaning the rim I found another eight cracks. Every forward pointing spoke on the right side had the same problem.
The wheel had been relaced in Cuenca, Ecuador and had been done far too tightly.
Luckily Fabricio found a smuggled black Excel rim the right size which I'll pick up today.