The manual's answer is the safe one. In aircraft, you NEVER reuse a cotter pin. That being said though, in car applications, like the front wheel bearing retaining nut, I've been known to reuse a cotter pin. On my bikes though, I ditch the cotter pin for a hitch pin clip... but after having one stolen off my bike once years ago (I guess someone else thought it was a cool idea, too), I safety wire it in place so it can't be removed by the casual passer-by.