I fill my diffs up all the way, reasoning is that by adding oil to change the diffs action it should be filled 100% so that the diff remains constant. ie, fill it up 50% the oil will be moving around inside and not providing a constant viscosity.
instructions on my car say either use hobby grease(which comes in the kit) or use the oil(option). The reason I ask the question is that grease and oil are very different and I'm worried there wont be enough oil on the parts at any one time.
I wouldnt even build up the diffs with the stock gears. I did and after 1 race day they were destroyed! Go and buy the Kawahara steel diff gear option about $100.00 , good luck upgrading that car it cost a lot of $ to make the car competitive. I have 1 for sale I was completely disatified with the Kyosho, I will not stray from my Mugen again!
HOBBYWING NORTH AMERICA /FALCON SEKIDO/ TEKNO RC TEAM/VBC Racing America/VP-PRO RACING TIRES/2010 R.O.A.R. VTA National Champion Driving a T2R PRO/NANO-TECH Batteries Paul Rush