I was concerned about my 65161 motor getting corrosion on the inside so I wanted to fill it with mineral oil.
Rather than opening it, I ran the oil down one of the phase cables. It took about three days for 30ml of oil to wick down the cable, but it worked and ended up inside the motor.
The process is simple, you slide piece of clear tube over the phase cable, it need to be tight fitting, fill the tube with oil and elevate it as high as you can. Mark the tube with a marker pen and watch the oil slowly go down.
I used sewing machine oil. I think it made the silicone of one of the wires go a little soft though, there are probably better choices. I recommend doing a test on a piece of the cable first to see if there is any swelling.