Originally Posted by FirestormX
Only apply as much lube as you need to coat the surfaces (bolt carrier group and buffer tube, for the most part). Otherwise, you wind up with a gun full of gunk that cannot perform. Aside from the lube itself gunking everything up, lube holds onto dirt, so you'll have dirty gunk, gunking your gunky internals that work best when not gunked.
You only need a couple of drops of silicone oil in the propane adapter every few fills as well. You don't need to create a pool of oil in the propane tank head. :P
Obviously you shouldn't be putting on globs of lube, I'm sure he's smart enough to realize that. Just a coat of the good stuff on moving metal to metal parts. Lube upper, charging handle, bcg, buffer, buffer spring (really not neccessary to lube buffer tube tbh), I like adding a very small amount of heavy weigh silicon oil to the trigger group after oiling nozzle o-rings, but that's about all the parts you need to go over on an AR patterned GBBR.
That said, I've never had a GBBR "gunk" up... maintenance wise, after every game or use, you should be cleaning it out completely, doing a quick inspection of all consumable parts, replace any if neccessary, relube with the quality synthetic stuff, then store it in a clean environment until the next game or use.
If you're the type of guy who never cleans your GBBR's, or does it infrequently, then obviously you'll be accumulating dirt and debris, or "gunk" in your gun. I've seen numerous examples of it happening and it pretty much breaks down to people being lazy. Lube properly, clean frequently, and you'll never have "gunk" in your guns.
Magazines should be inspected regularly as well, and seals redone properly as most come fairly crap from factory.
As for adding oil, if he gets the AI oil pump kit, then he only needs to oil it once for the life of the tank. Saves you the hassle of putting drops of silicon oil in an adapter head and getting it everywhere if you're not careful.