bearings of rpm revo axle carriers
 

I have open the cover of the bearings.
Then, I have seen there is no grease inside. Only light oil inside.
Moreover, the covers are not very tightly fit as Traxxas are. The play is large. I can see the inside directly.
I concern the shielding from dust is not very well and the life could be short in lack of any grease inside.
I clean the bearings and put some grease inside anyway. This adds some drag to the bearings.
How do you guys think of this?

bearings should be only oiled lightly not grased. grease adds friction.

I am not a racer.
Adding slight friction is not my primary concern.
I want bearings to be carefree and long life.
That is why I don't get that Rpm make the bearings this way.