I'm trying to change the oil in my transfer case. I believe it is a 203. I have the 2wd low range, does that mean it has to be a 203? I know it's not a 205 but I don't know what the 208 or 241 look like. Anyways, I need to know what type of oil to use in it. I heard that they use motor oil but the oil that came out of it looked (and smelled) an awful lot like 90w gear oil. Also, how often should the oil be changed?