I bought from halfords nissan to ISO leads and i cut the ISO bit out and wired it to the stereo wires . I had exactly the same stereo.
(I did that just to not cut car's wires)
Hello
It is very easy to change the oil, I'm not sure about the problem with the shifting the gear stick.
If you still need advise and instructions on how to change the oil i can help you just let me know.