Seems like it would be easier to just keep those spare parts as you described earlier.
And there is the difference between an engineer and a chemist.

It probably depends on how easy it is to acquire and replace the parts. I would think a big-name generator would have spare parts available while with some no-name Chinese gen this could be an issue.
My friend's generator was acting funky for hours before it quit. This suggests one would have some warning and could make the repairs without being under pressure/in the dark/whatever.
-Blast