The leak is coming from the gear box/transmission. You will have to replace the gear box to repair the leak.
There are two different seals they leak from. The one is on top the gear box and the other is around the motor coupler shaft on the front side of the gear box.
If the top seal leaks it often gets the clutch oily and then the washer does not spin good.
Being you said your washer is running fine I would guess the leak is coming from the other spot around the motor coupler shaft.
If it is leaking oil from the motor coupler shaft the washer could run for a long time without it ever hurting anything on the washer.
As for a manual, here is a general manual for all direct drive washers that were made by whirlpool.
The controls will be different then your washer, but the working inside parts, such as the gear box, clutch, motor, coupler, etc... will be the same.Direct Drive Washer Manual (2.78 MB pdf)