I have a 2001 1.6 Brava SX and need to replace the automatic transmission gearbox. Is it better to get a used one or a rebuilt one? Soneone told me that a used one, even with low mileage, cannot be counted on for long because the rubber seals inside may be dried out. But a rebuilt one, he said, should last as long as a new one.

Common sense really. A used one left to stand could be seized and you have no gaurentee.
Generally with reconditioned engines and gearboxes you will get a guarentee and the box should be in good condition and should last. But it will come with a premium price.

The question is can you afford a reconditioned one or do you want the gamble?

used will be a lot cheaper so i would take the risk.

which 'rubber seals' is he reffering to?

Actually the price I got for the used one was only a little less that the reconditioned, so I chose the latter. It is being done now. I feel good about the choice. I don't know enough about the subject to say what the seals are. But he showed me some rubber rings.