They usually have grease or fluid. My monsoon looked like it had grease and my hurricane looked like it had fluid. I do not think you would notice it too much for bashing. I usually do not run my cars anywhere else but the track so I cannot say for sure.

By the way I finally changed the diff fluid in the rear and it was a little better but still spun alot. I called the shop I bought it from because he has one he races and said for me to put 20k in the center that 10k was too thin that it is not distributing the power evenly to the front and back . So thats my next project. Update when I am done.