kato diesel locos don't need maintenance. they will run for dozens of (real) miles without any work on them.
They may not NEED any but I would clean the wheels to maintain good contact and very lightly grease the drive gears.
However if you are going to grease the driveline gears, you should take it apart and clean all the old lube out. Its better to have less lube than too much.
I use a little oil since I have so many locos. As I found out the hard way grease dries over time. So I never use grease.
