I started with a putty knife and worked up to a screwdriver and then a bigger one. If I had some help holding the housing it would have been a lot easier. That is a messy stinky job you are about to dive into. :: fd
There are soft washers under each nut that must be cut or pried off. At times one will leave a little piece in the threads. After removing all of the washers, leave a couple of the nuts slightly on (you don't want something that heavy to jump out) and gently pry the case. First put a pan under it to collect the oil. After it is loose and the oil has drained remove the two nuts and pull it. Be prepared for the weight.