Took mine in checked baggage to the US and brought more home - no problems either way. If you are taking car kit on 'planes, one tip I would recommend is to put a big sign in the top of the bag saying "Radio control model car racing parts and tools" and a copy of a magazine that has your car type in it.
If customs or security decide to open it, they first see your sign, and then the magazine, and that helps them see what is there and why it is there. You'll get problems if there are any flammable liquids (buy tyre additive and motor cleaner when you get there, and leave it there!), anything in an aerosol or if things are not securely packed in boxes. IME they rarely open the bags, but if they do, best to be prepared. HTH
