I guess the rear axle is from an old car. They usually had a plug on the back sheetmetal cover or a plug on the side of the casting. Most of the time it was a 3/8" square drive to remove it. Check the bottom for a plug too. The side plug is for adding fluid and checking level. A bottom plug would be for draining.
I would check for the bottom plug first. If there is one, I'll teach you an old shade tree mechanic trick. With an old machine let it sit for a few days. This allows water to settle to the bottom. Back off the drain plug until it is almost out. Water is thinner than the oil so it will leak out with out much oil coming out. Once the water stops draining, you will have to decide if there was alot in there. Use 4 ounces as a guide. Alot could have gotten to the gears. At this point it would be best to open up the rear and clean it. If it isn't alot, tighten the drain plug and check the level at the side plug. You should check the other fluids too. Contaminated oils will smell it there is gas in them or look milky if there is water in them.
You should drain and clean the fuel system because old gas can cause problems. Good Luck
Edited by boyscout862, January 22, 2013 - 02:45 PM.