If the fluid has been in there for a long time, I would consider loosening all the bolts, cracking the gasket from the surfaces and let it drain from the bottom. Then take off the cover and do a visual inspection of everything in the rear end. That way, you can make sure that there are no metal shavings in there and wipe the insides squeaky clean. It's worth the price of a new gasket and a little bit of your time. Most NAPA stores will have or can get the gasket for you in a day.
