Blown Golen 4.6

[Jonaspdx]

I bought an 01 XJ with a Golen 4.6 stroker with less then 15k miles on it a few months ago. When I bought it, it had a miss 1 & 6, took it to the dealership to get it inspected, and was told it was due to a crack in the intake manifold. The guy I bought it from had a ton of other jeeps and was diagnosed with terminal brain cancer and needed the money. he kept pretty meticulous service records and gave me a binder with everything he'd done to the jeep. I put on a new manifold and the jeep ran fine, not great for a bit then started missing pretty bad. Only really missed on decceleration, cylinders 1& 6. Threw some parts at it with no luck and I took it back to the dealership, they said it was leaking from the manifold gasket pretty bad, tightened it all up, still leaking. They also said that some part of my exhaust after the header had dissinegrated causing the o2 sensor to read wrong and run rich. They ran a compression test, great results, 175 psi in all cylinders but #5 which had 180. They did a leak down test which showed cylinder 1: 20% leakdown, 2: 18%, 3: 22% 4: 20%, 5: 14% 6: 30%. They also said all leakdown was from the crankcase and they were pretty convinced it was from piston ring issues. I was pretty suspsiscous as Golen is such a trusted performance shop for the engine to fail and have such excessive blowby at only 15k miles, especially with meticulous maintenance. I theorized it was a valve timing issue possibly caused by the cam synchronizer and the tech responded: "its pretty unlikely with that style of motor because at top dead center(for the leak down test) all of the valves closed as they should on each cylinder. You have excellent compression but on the "bang" stroke, the blowby is excessive to say the least. It is also very very unlikely but if the piston rings were all lined up it would also cause excessive blowby. Again, very unlikely on 5 0f 6 cylinders." Should I seek a second opinion before doing another rebuild? Anything I can do to confirm it needs a rebuild? I contacted Golen earlier today but was unable to get through, I left a message as well as email and am waiting on there response, hopefully I can ship it out to them and they will rebuild it. 

[amcinstaller]

If you can, see if anyone can borescope the cylinders before you pull the head. Also, do you have access to scan tools with live data reading? See if you can find it what the pcm is seeing/thinking. The only thing that seems out of place is 30% leakage on 6.

Also, the rings will float and rotate during engine operation. Placing gaps at offset during install is best practise but doesn't guarantee they'll stay where you left them. As well, your o2 sensors closest to the engine tell the engine how much fuel it wants. Does your jeep have the pre cats on the exhaust manifold? Where are the upstream o2s compared to those