I often visit an antique shop that sells gadgets like old cameras, equipment and lenses. I'm particularly interested on buying an old macro lenses from Sigma, Ricoh, and Nikkor. I would expect the following conditions when purchasing an old lens:

1. Manual Operations
2. No electronic contact
3. Compatibility issues (which I am aware of)
4. Manual Focus (not an issue since I'm targeting a Macro Lens)
5. Dusts inside it (since it has no electronics, I guess just cleaning it will do, professional service maybe)
6. On a Positive note, the build quality is arguably better since most of it is Solid.
7. Cheaper

So what should I do whenever I purchase old lenses from 1980's to "Restore" (if that's the correct word) the whole item? If there's anything that I should checked before purchasing it, what are those? Thanks!