Here is the stuff I use:
http://www.amazon.com/Gardner-Bender-OX-800-Anti-Oxidant-Compound/dp/B000BOCBCA
I usually get it from Home Depot, they seem to have a decent price on the stuff.
It can be had in various sized tubes, the one I gave you is pretty huge, it would last me for the better part of a year.
I have cut the nozzle of the tube large enough that I can stuff a #8 wire into it, which certainly coats the wire pretty well.
For large stuff I just squeeze it out as if it were tooth paste, and smear it all around. You can also drop a dab into a lug that is going to receive a large wire.
Often enough I get called out on trouble shooting that gets me opening a panel. I just as a matter of course check the wires as best as I can, the white ones especially. If there is any sign that the wire has been stressed, I might back off the screw, pull the wire out, cut back the burned bit, expose fresh copper, and give it all a nice goosing with anti-ox.
And I stuff it up the breakers where they are going to grab the buss bar. Make sure it is not slopping all over the place, as it conducts electricity.
It has two wonderful qualities: it keeps the oxidation at bay, and it maximizes conductivity. These are GOOD things in an electrical panel, assuming you don't have it bridging from one leg to the other. Oh, and improved conductivity means less heat at that point. Very good thing.