Case 1150 B model dozer track problem

Have a 1150 B model dozer, around a 1976 model I think. The left track will not turn, and some how oil is going from the transmission into the rearend. I know this because when it quit pulling, I checked the trans and put 5 gallons of oil in it and it still would not pull. I got it to the garage, checked the trans and it was low again with no signs of a leak, I'm assuming it went into the rearend. Any help would be much appreciated.