Instad of brake or carb cleanerer, I use some stuff called "Gun Scrubber"
I actually use this for my firearms, but it works great on RC stuff. Leaves no residue, or scent.
There is two versions of it though, so be carefull. If you want to try it, make damn sure you get the "SYNTHETIC SAFE" version. It is made for using an plastic parts, and will not damage them. If you use the original, it will melt any plastic you use it on.
This stuff will get anything off, even hard, caked on, dried carbon residue that was been building up for 30 years. Best stuff I have found.