IMHO I would not take a motor apart unless there is something wrong.
You know I had to do that with my Tongxin
here as you did too Pedalo.
When I did there was plenty of grease inside, but as one of the springs on my the clutch/freewheel had got misplaced and was making a terrible noise, it had to be sorted. I was pleased it was just a displaced spring
Getting some of these motors apart is not that easy and usually requires a special tool, which in my case I got someone to make for me. It also allowed me to sort out motor and cut down the long motor shaft I had, it being a motor made for a roller brake fitting.
Some of the motors with hall sensors have quite fragile connections inside, which again risk being damaged unless you are carefull.
Now that I can take Tongxins apart I may consider a regrease after 3-4K miles but on an annual service, just take the wheel out clean up motor shafts either side incl fittings, maybe put a little grease around the outside bearings either side but that is it.
Regards
Jerry