I removed the front wheels and gears on axle that drives the front wheels. Take off the cover over the drive gear box. Remove the 4 bolts on each corner of the gear box. I had to take out 3 that were easy to get to then use a screwdriver to pry gearbox to one side so socket would fit over remaining bolt. Then remove lower casing and remove the yoke that engages the drive by just pulling down on it. The assembly then just comes apart and out. Watch for the Pully next to the gear does have a D-key that may drop out.
My Helical gear was worn/dished out P/N 137050 $7.99 compared to below whole assembly.
Power Drive Gear Box Assembly 702511 $82.49
Worn Helical Gear 137050 $7.99
Worm Shaft Gear vertical 137051 $17.04
Bearing for worm shaft gear 77881 (Qty2) $2.99
Clutch Pulley 750436x $3.92
Bob, September 2008