My used 3H gooseneck only came with one safety chain.  Should I get another chain put on or is one enough?  I always thought it was safer to have 2, especially with a bumper pull. Does the same go for a gooseneck? 

Also, someone told me that the ball should be greased - they related a horror story of the ball snapping off someones gooseneck from friction because it wasn't greased. What kind of grease, how much do you use and how often should you grease it?

Most GN trailers have two chains.  The requirement (from the DOT, I believe) is the chain strength should be equal to the gross weight of the trailer.  A 10,000 pound chain will be pretty stout and "Heavy"

I don't see how the lack of grease will cause a ball to snap off.  Wear the coupler and the ball to the point of the lock not holding the ball... maybe.

Use a grease with an EP (extreme pressure) rating.  absent that, any clean grease is better than none.

We use 2 chains and grease the ball (gooseneck and BP)  The weight and friction on a dry hitch theoretically could cause enough heat to crystallize the ball and make it susceptible to metal fatigue and lead to being brittle = a possibility of shattering......so it is said.

Tell me more about friction heat crystalizing the metal.  I don't see how enough heat can be generated to affect the mass of the ball or the ball neck.  The truck frame and hitch should act as a heat sink.   Further, heating steel tends to anneal it, leading to softness not brittlement

Regardless of long term ball/ coupler denigration - I can't stand the sound of the grinding as I travel over rough roads and turn corners. If it makes noise - grease/oil it.

I have a can of black grease (??) and I put a tablespoon or so of that up into the coupler.

If you take your truck through a car wash with dingly-dangly things - be sure to tie a plastic bag over your GN ball so you don't transfer the grease to the dingly-dangly things.

YES - 2 CHAINS. If your trailer pops off the hitch (god forbid - but I know a dealer that forget to lock his coupler one time) you want EVEN chains to stop it.

PLUS - make sure that your emergency brake cable is at least 1 inch shorter than your chains so the brakes come on before the chains suck up the trailer.  Then, make sure your chains are several inches shorter than the hitch to the tailgate measurement. The worst thing is to yank off your tailgate and have a GN trailer hanging by it's chains at the back.