Here is a post I got off Pirate...
"Go find a local hobby shop or R/C race track and ask the kid behind the counter for a couple bottles of 5000 or 7000 cst silicone diff oil. It's available all the way up to 100,000 cst. You should be good with the 5000 or 7000, 10,000 may be a little too much especially for a 4 cyl. i.e. more lock up that takes more HP to run. Be gentle on the o-ring when you take it apart since its 20+ years old."
