stupid question.... answer needed

so the proper way to check the level is stick your finger in the hole and it should be up to the first joint of the finger. That seemed a little high to me but I have never dealt with one of these rearends. This has a 1/2" square plug but I couldn't get it to break loose the last tome. put a 1/2" impact on it and still didn't come out. I am going to remove the cover Monday and heat the plug and see if that will do it. Just bought this car end of last year and have not driven it much at all and need to check this out. thanks for the info.