The rental/instructional airplane was found with substantial damage during a post flight inspection by the airplane operator's maintenance personnel. On the day before the damage was discovered, two pilots, each of whom had separately flown the airplane, reported airplane discrepancies to maintenance personnel. The first pilot reported a discrepancy with the tire sidewall that he noted during his preflight inspection. The airplane was retuned to service after the wheel assembly was replaced and no further inspection was performed. The pilot then flew the airplane and returned without any further reported discrepancies. The second pilot reported a binding in the control column and could not reinstall the gust lock without difficulty during his preflight inspection. Maintenance personnel then grounded the airplane for the day and found damage to the airplane firewall.