THE AIRCRAFT GROUND LOOPED AFTER TOUCHDOWN. THE PILOT REPORTED THAT THE LEFT MAIN GEAR TIRE SUSTAINED A BLOW OUT AND HE LOST DIRECTIONAL CONTROL. INVESTIGATION REVEALED THAT THE LEFT WHEEL TUBE VALVE STEM BROKE OFF AT THE BASE DUE TO DRY ROT. THE TUBE REPORTEDLY HAD 1,200 HOURS SINCE NEW. THE AIRCRAFT HAD AN ANNUAL INSPECTION 7 HOURS AND ONE MONTH PRIOR TO THE ACCIDENT.