Just a wild guess from someone who has no knowledge of THAT particular generator, but could it be that the winding gets too hot? Perhaps air vents are clogged or something??? I was part of the engineering team at a company that rewound large motors and generators many decades ago, and so I do know a little about the materials used in generators in general, and heat is what kills most of them, either high heat for a short period, or low heat for longer periods. That this one failed that way suggests the adhesive/plastic may have overheated.
BTW, this query has nothing to do with the Forum. I'll notify a moderator and ask it be moved to a more appropriate forum, where better answers might be forthcoming.