I just overheated my trans while backing up the heavy trailer. Truck had also just pulled that load around 50 miles up and down several mountains at highway and interstate speeds so the fluid was hot. I learned my lesson and I have never had the problem again and I have backed up much heavier trailers since. I also have auto lockers in that truck, I just have to watch how I back up in low range to keep from binding the drivetrain on hard pack. This was just my experience, you could have a front seal problem if it is happening while just normal driving.
For the oil, as others have stated, it is probably coming form up top of the motor. Look in the valley under the turbo. If you see any puddles of oil you need to look around the engine bay and see where you see fresh oil. You may need to clean the motor first let it dry and then start looking.