RE: Question for first truck
Maintaining them is pretty straight forward. Take the bearings out, clean and oil them once a month or after every time you run in the rain or mud. A drop of light oil on every metal part is also a good idea about once a month.
If you're dealing with brushed motors then pulling the motor and cleaning it every couple of runs is pretty standard. Oiling the bushings every run or two is also a good idea.