Toyota Repair: Toyota catalytic converter aftermarket part, camry xle, toyota catalytic converter

Question
My 1999 Camry XLE has about 58000 miles. In 2/08 I had the catalytic converter replaced with an aftermarket part. About 9 months later the check engine light came on (again). This time they said it was a thermostat. I had it replaced. The light came on again. The mechanic said it was an oxygen sensor ($230.). That was replaced finally, about 10 days ago. 6 days later the check engine light came on again. This time the mechanic scanned it and showed the catalytic converter needed replacing. It cost me about $900. He said the other one may still be under warranty in which case I pay only for the labor. He said if I get another aftermarket part it may last 6 months, or it may last much longer. If I get a Toyota cat it would cost me the difference between what I paid for the aftermarket cat and the genuine factory part plus labor, about $800. My car has a book value of about $5000. Is it a good idea to plunk down another $900 or so for a genuine part? How long is that going to last? Are aftermarket parts inferior. I can't afford a brand new car, so if I replaced my car it would have to be with a used one. Thanks for any advice you can offer.

Answer
The 1999 camry actually has two catalityc converters, there is one attached to the exhaust manifold which is the main cat and is usually the problem, there is another "sub cat" lower in the exhaust pipe which rarely causes the problem, can you tell me which one was replaced? Can you let me know what the trouble code is at this time?