You don't really need a leakdown - it only has 15 PSI anyway. All you need is a tool to hook an airhose to the cylinder. I made mine years ago by breaking the ceramic out of an old plug and welding (or brazing) an airhose chuck into the metal shell. I have heard you can buy a tool like that today, but I don't know where.
Replace the spark plug with the tool and hook up the air to it. I usually knocked the pressure down with a regulator. You don't really need 120 PSI with a hole as bad as yours. Listen at the exhaust for hissing of air to indicate a bad exhaust valve. Pull the lid, MAF, and bellows. Open the throttle and listen for hissing to indicate a bad intake. Pull the oil filler cap and listen for hissing to indicate bad rings, hole in piston or whatever. Yes, the sound should be noticible with only 15 PSI compression.

If a gasket is blown into the water jacket, it will want to barf water out when runnning, or at least bubble the water in the radiator. It may be more difficult to see with the cross flows of today than the old style downflow. I don't know. It has been years since I've done this. If a head gasket is blown into a water passage, it may also be putting water into the oil. Not sure on an LS1, but it can happen on other engines. In that case dino oil will be tan and foamy. Not sure how synthetic reacts.

I'd be surprised if you could get only 15PSI compression with a hole in a piston or a broken valve spring.

 

What's with this hole in piston stuff? I'm not hearing any loud noises, just loss of compression and some oil on a plug, I want to say it's a spring or a valve from the info I have gathered, if it was a piston, i think I would hear it. The rings probably aren't bad, I haven't abused the car to that point.
Anyhoo, I am taking the car to a shop to see what is up with it.
-Steve

 

Why don't you just pull the valve cover and check the springs on that cylinder? Save yourself some time and money.

 

yeah I am going to do that.
After that, which I don't think it's a spring, it looks like the head will have to come off =\
-Steve

 

Was there smoke pumping out of your oil filler cap at idle?

 

It's a broken spring, I haven't started the car because of it.
-Steve