I had one of my alloys cracked not so long back thanks to a rather large pothole. Luckily though, it was repairable so took it to a bloke called Sev (quite big in the Ford circles for aluminium fabrication) and he angle grinded the cracks out and rewelded it. The lads at the tyre centre didn't think it would be ok but were very surprised when it was only 5 out on the balancer. Basically, if this had happened to one of your wheels, but was repaired badly, that may be why it's so far out. Inspect the wheel to see if there's any evidence of it having repair work done.

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Quote Clarkson, Top Gear, 17th July: "I'm not having a stroke... just driving a Nissan!"
Quote Ry, Mallory Park, 3rd Dec:
"Ahhhh crap... Just a bit too over eager really!""I used to be an adventurer like you, but then I took an arrow in the knee"