Is he referring to the neutral/ground bar?
All the busbars- neutral, hot and ground. The breakers will snap into the busbar, you want paste between the two, so you just need to paste the breaker contacts.
Likewise if one wants paste in their receptacle you don’t need to squeeze paste under the screws into the clamps, just paste the wire and there will be paste between wire and clamp. If you are going to this extent take some emery cloth and clean the oxidation off the copper wire ends first.
I know they pasted the aluminum cable that enters the new 200 amp panel I had installed a few years ago, but that would be antioxidant paste one needs to do when connecting aluminum to copper. Here BC Hydro does not use copper cable from the street/pole to new houses anymore, they use aluminum.
I am not sure where to put the junction box? I guess you would have to cut the dry wall out and mount the box to a stud close to the outlet, kind of like in new construction and then patch some new dry wall in?
Yeah, but as long as you have accessible cover on it, and not buried behind drywall. Think of it like a sub-panel mounted inside the stud cavity. Yeah, could be fugly. I think 10 gauge is more than sufficient.