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?