Oil under the washer is not a good sign. The first thing to do is to disconnect the washer from the wall outlet, remember that safety should come first.
Remove the front panel of the washer. To do that, you could use a spatula to release the front panel holing clips. These clips are about 3 inches from the sides of the front panel. Insert the spatula between the top and the front panels and push the holding clips until they release the front panel.
Remove the front panel and use a drop light to illuminate the area under the washer. If the oil is leaking from the transmission seal, it will be all over the transmission pulley, the belt and the clutch assembly.
The correct procedure will be to replace the transmission and the belt. That in my opinion is too expensive to do, probably will be better to get another washer.
Now, if the oil leak it is small, what you may be able to do, it is to remove the belt and use degreaser to clean the transmission pulley, the belt and the clutch. Then reinstall the belt and adjust it. This may buy you time before you need to buy a new washer. Use baby powder to dry the belt before installing it.
I will not worry much about putting any oil in the transmission, jus run the washer it until you can't use it any more. Install the front panel and try the washer to see if it works better. These washer are not made like the older ones, you are lucky if the washer last you over six years.
I see many customer do this and get at least a couple months on the washer, before having to get a new washer.