Max 232
Probably you should apply for MAX220EPE that has wider operating temperature range -40°C to +85°C. In my opinion, if an IC has wider temperature range, it should be more resistant to performance degradation. Pls correct me if I'm wrong.
Assuming that all parts in the circuit work correctly, the IC should have no problem to do the job for ONE WEEK, which is not very long.
Furthermore, I don't think MAXIM or manufacturer will send lower quality product to customer for evaluation. The design of MAX232 is very matured already, so it should be bug free. If MAX232 is a new IC, then the sample might still have bug.