R2,
I'm thinking that if there is a solid that turns into a liquid above a certain temp then gravity takes over and it will want to pool at the bottom and leak out at the shooters end. The barrel nut will be on tight sealing the front so no leakage there. But, in your case it sounds like there's so little of it that it will just stay in place and solidify as the receiver cools. Even if it gets hot it will probably still be too viscous to run and too little of it to do anything other than stick to the surface area it's at. I can't see it being an issue at all.
I'm thinking that if there is a solid that turns into a liquid above a certain temp then gravity takes over and it will want to pool at the bottom and leak out at the shooters end. The barrel nut will be on tight sealing the front so no leakage there. But, in your case it sounds like there's so little of it that it will just stay in place and solidify as the receiver cools. Even if it gets hot it will probably still be too viscous to run and too little of it to do anything other than stick to the surface area it's at. I can't see it being an issue at all.