Newbie here so take what I say with a grain of salt.

Given that you are running a metal spur gear instead of plastic, you may want to lubricate it somehow. Is the pinion and spur enclosed? If not, a dry lubricant may be best to avoid attracting dust and dirt etc. Something like Rock N Roll Red/Absolute Dry (dry bike chain lubricant) may work well. It is likely that you will need to reapply it often.

Link:
http://www.rocklube.com/products.html

Honestly, I think I’d rather just run a plastic spur gear so I don’t have to worry about lubrication...