Lubricant grease based PTFE (polytetrafluoroethylene) better known as Teflon. Prevents wear of parts and is suitable for long-term lubrication since the layer of Teflon is adhered on the surface of the gears to filling the micro pores of the material. It can be used in any combination; metal/metal, plastic/plastic or combined between them.
Remember that the quality of the grease and that it correctly distributed is very important. Many grease is not the most important in making a correct lubrication. Put a small amount of grease every three or four teeth of the crown and moving you the transmision. The grease will be distributed regularly between all teeth of the pinion and the crown.