There is a pipe plug about 1/2-way down the case (I think on the DS then there is a drain plug on the very bottom rear. Take the plug out on the side and feel around for oil in the case if you cannot feel it add (through the same hole)until it just starts to come out the hole. If it has not been changed in decades you may want to drain it followed by a kerosene wash (refill with Kerosene and run it back and forth in the driveway a few times). It takes something like 2-1/2 quarts I think to fill it (should be in the owners manual). Good luck.
