I'm trying to do my first transfer case fluid change in my 231 and the fill plug is stuck tight. Also, it doesn't look like all the other fill plugs I've seen as it isn't an Allen key like they usually seem to be or even the 30mm head that a lot of people have mentioned. I can't tell if it actually is an allen key plug and there's something stuck in it or if it's some odd kind of plug that a previous owner used. 19mm is the closest I could get and even that started to round out the edges. Does anyone know what this fill plug is or have ideas on how to get it off? The fluid was really nasty in the transmission and oil was in the engine too so I'd really like to get that stuff out of the transfer case since I'm guessing it's just as bad.

