Hey, be sure to keep us posted with what you find to be wrong. I have exactly the same problem with mine. It looked allright on the bench in the diff head, so i threw it in, but like you, found the bloody thing won't unlock.
Its odd, i can leaver the dog apart from the coupler through the filler plug in the diff, so there is enough clearencel, i have tried LSD oil, no change.
I haven't pulled it out yet as i have been waiting to hear from someone that has had a similar problem and what they did to sort it out.
So i am most interested to hear..........
