Found this for you,. second comment down
http://www.fixya.com/support/t1896160-loss_drive_in_craftsman_lawn_tractor
I also have a Craftsman tractor with the same problem. Sears repairman said it needed a new transmission and it would cost $1,400 to install. A new one is about $1,000. Anyway, if you remove the battery and the battery tray under the seat it will expose the transmission fill hole (hex). I opened the top and it looked empty. I had a bottle of 90 weight gear oil in my shop and filled the transmission to the top. I have not had any problems with it since. $4.00 bottle of oil verses a new tractor is worth a try
http://www.fixya.com/support/t1896160-loss_drive_in_craftsman_lawn_tractor
I also have a Craftsman tractor with the same problem. Sears repairman said it needed a new transmission and it would cost $1,400 to install. A new one is about $1,000. Anyway, if you remove the battery and the battery tray under the seat it will expose the transmission fill hole (hex). I opened the top and it looked empty. I had a bottle of 90 weight gear oil in my shop and filled the transmission to the top. I have not had any problems with it since. $4.00 bottle of oil verses a new tractor is worth a try