hello i have bush hog squaler sq480 4 foot trying to keep it matntained i have a box deal i think it is called a gear box how much oil and what kind of oil do i put in it it has a threaded plug on top and a drain plug on the side by the bottom i put i hose to measure it it is about 1/2 about the plug on side is that enough or do i fill it up more please help.