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 ,can I mount Troika on this arm version I can't see third hole on the pic.