I wouldnt pack bearings as it cause more drag and collect dust and dirt. A drop of motor oil would be better in most cases but I dont do that either. Advid.com has all bearings for $1.00 so I just replace any bearing thats not smooth.
If I was running threw water or snow I would pack with greese but im only racing my RC's so I dont...
White stuf on screws could be corrosion or loctite