I've had the same problem more than once on an otherwise strong mower. Right side still powered, left is free-wheeling, sometimes locked up. Bad design of plastic gear teeth on the inside of the wheel against the metal gear.
Also, the bushing/bearing that runs through the mower deck / chassis and into the wheel assembly housing is J-U-N-K. My left wheel broke almost off last week. I am meticulous with caring for this machine, and was surprised to see the bearing had come apart, and the drive axle had been misaligned for so long, it was worn almost through.
After replacing both front wheels, 2 e-clips, and now what appears to be an entire front drive assembly, it's probably time to move on. I'm only upset that the engine (190-cc) is so strong. Never any problems at all, and never more than 2 pulls to fire her up.
Anyone need a very strong engine from the (917-376160) model mower?
brian_strack@hotmail.com
Good luck!