I removed and disassembled my driver's seat, and confirmed that the gears on each side of the reclining lever were correctly meshed with the adjustment shaft (pics below). The seat spring core, backrest frame, and all hardware are in great shape. The only thing I found amiss was one of the rubber rings around the adjustment shaft had worked it’s way out of the channel on the seat frame. This particular rubber ring is circled in a picture I found on this forum (complements of Achim) and I doubt it would affect the amount of recline by any noticeable amount. At any rate, I squeezed the rubber ring back into place in the channel and reassembled the seat. I intend to reinstall the seat this evening.