OK, so the motor is lubed, the braids are set but you're not quite ready to race...yes patience grasshopper.
Below you can see the gear from a Sloter Zytek kit. There is a tiny bit of white lithium grease on the crown gear but hardly any in the self centering channel of the gear. For the gears this might be an adequate amount of grease, but for the channel that centers the gears (where the shaft from the motor rubs to provide the centering of the gear) you really need copious amounts of grease.This are has a lot of friction, especially if the shaft is a bit off center and rubs on one side of the channel. And if you have no grease at all you will get brass dust around the area and your gears WILL wear out quickly. Don't run a car without grease...especially a high performance car like this Sloter, a Slot It...well anything really.
Here you can see a sidewinder gear from a Sloter/MB Slot Racing Ferrari 312 (hmmm, Sloter photos are jumping onto the front page tonight for some reason I guess). And as you can see it's completely dry.
With cars with plastic gears (though the pinion gear is metal) like this one it might not be as critical that you grease the gears but basically it's a bad habit to get into in any case.Here you see a chassis from the Scalextric Jaguar, it's got plastic gears all around. The car will run ok without grease, but it will run slightly faster with the grease, and it will run noticeably quieter.
Will your cars run without greased gears? Yes...will they last as long as they should if you don't grease the gears? NO...