It all depends on what car you have and what track surface you intend on racing on. It's probably worth checking with the guys at your local club and seeing what the general consensus is.
If its KF1/2, then generally you'll run about 400-450 CST front and 300-400 rear, depending on surface. Thats like 30-45wt.
Gear diff wise, the average seems to be around 10,000 CST, some lower, some higher. If its a slippery surface, most opt for a ball diff.
I tend to use CoreRC oils.
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