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@DarkBlack I'd bet it came through the junction box.
As it is an induction motor, it is only going to possibly going to arc/spark when the windings fail, but I do think
@MAX-24-Dean makes a great point about why it is worth cleaning the housing out and improving the sealing. I've seen the results of motor induced explosions and the results certainly make an impression.

I would replace the felt seals on the shaft (just a guess. Many older motors had them. Did it have any / is there room for them?), sealing it up with some sealant when you reassemble the housing, and I would switch to water/dust tight cable glands / clamps.
Let us know how the saw is after the overhaul!
All the best,
Peter