I googled it, it is discontinued at AMAIN Hobbies, so it must have been safe for the RC environment. Search the forum for Sealing A Nitro Engine for more info.
Generally used to seal carb neck, needle valve assembly, carb cinch bolt and back plate.
Green slime would be good on any o-rings that are intended to seal to prevent the seepage of fluids around moving parts. Silicone sealant is good for surfaces that mate and then do not move.
The associated green slime not only helps with sealing the o-rings, it also helps preserve them if your rig sits for a long time. Over time, the o-rings in the carbs dry up and shrink. Especially when the engines aren't used. They get dry and brittle.