LINN: What should a buyer know BEFORE buying a preowned Ittock?

Buying such a delicate component as a tonearm SH not easy,and not without risk,they are 30 years old...What should I now,and what is MUST check,or must ask.Is there big diferense in sound betwen LVII versions,is latter a single counterweight better sounding tonearm. What will be your bid for this one http://www.ebay.co.uk/itm/Super-rare...item2320a480e2 ,can I mount Troika on this arm version I can't see third hole on the pic.

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