The grease's intention is for metal to metal to plastic contact. You don't need a lot, put a little on the gears, spin the transmission up and you get an even coat on all the gears, I tend to pull the box apart afterwards and clean off be excess that's forced out to the case.
If your worried about a little stiction by running this, remember the motors we use are plenty powerful and what stiction there is in the transmission is minimal, certainly not detrimental to performance.
Or do as a few others have said and use diff gear oil, which its purpose is to cause internal friction between planetary gears to give a specific rotating action.
Each to there own and I'm sure everyone has there own way of doing this, this is just my take on it. I find if something is designed for a certain use, it generally is the best method.
I now use this Hiro Seiko after I ran out of Tamiya anti-wear grease. Hope that helps.
http://www.rccarshop.co.uk/index.php...ar-grease.html