Yamaha XTZ SZR 660 motor - achilles heel?

[A100man]

Hi

I've gotten interested in acquiring a 660 single from Yamaha or maybe MZ but I note form the forums there appears to be an issue with the counter balance shaft gear/key-way that can self -destruct and grenade the motor in a worst case.. Anyone know if this is really a serious issue?

There appears to be a fix if you catch it in time (which still involves a fair strip down) , but I'd rather not put myself through the grief if the claims are exaggerated.
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[Tdibs]

Pretty sure they are well regarded for doing large miles in the 660 tenere's. Pretty much any of these big singles have their weakspots, the 660 seems better than most to be honest. Would just look out for regular servicing.
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