hitting a pothole wont cause that.
in fact, it looks fairly new, as the grease isnt discolored yet.
in the case where the boots already torn open, i recommend the entire axle be replaced.
any good auto parts store (napa, autozone, etc) will sell you a fairly reliable aftermarket rebuild for a LOT less than a 600 dollar factory one.
probably more along the lines of 125 bucks. at that price, it would be silly not to replace the whole thing.
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