The description of the failure is not specific enough to say for certain, but this sounds like it could have started as a turn to turn failure within one of the stator coils and eventually deteriorated to the point of failure to ground within the slot. Why it would have passed the surge test is...
Here is a US company that can also supply this. They also offer small quantities so you won't have to purchase an excessive amount of material.
http://swwireco.com/
