Ok where to start....Bought a C5 from a local road race guy (was looking for a c5 for road racing) that was pretty known within the local community. Motor only had about 2500 track miles on the recent rebuild.

Here are the basic specs of the car (I can dig further if you want):
383 stroker--
Eagle rods/crank
Diamond pistons - not sure of compression ratio the motor is running
Mild comp cam
Old unknown AFR heads
Blackwing intake
Stainless works headers
Borla exhaust (still running cats)
Catch can
Makes a mild 430whp/450ftlbs

Before the rebuild the motor and heads were "gone through" and typical things were replaced, valve seals etc.

Main issues:
-Black soot on the back bumper (I could honestly care less but it has to do with the amount of oil i'm burning)
-Consuming oil badly (haven't got a good milage readout yet) 600-700 miles for 1-1.5 quart is my guess.
-Puffs a little plume of smoke on startup but clears up quickly
Video: -Looks like it blows oil out the exhaust when at high RPM

Had the car retuned a few weeks ago and the tuner said everything looked fine.

Then I took it down to a buddy's shop where he performed a leak down and a compression test. Here are the results:
1: 200psi/10% 2: 180psi/15% 3: 200psi/10% 4: 205psi/15%
5: 200psi/10% 6: 175psi/20% 7: 175psi/20% 8: 200psi/10%
These results were not ideal but there is obviously some kind of leak somewhere. Again, really hoping valve seals lol.

My guy pulled the plugs and said most of them were fuel soaked (this threw a wrench in the mix, unless it was actually oil), which points to the running rich thing which can obviously cause rings to fail over time. If that were the case there would still be an issue somewhere with the fueling then that the tuner is unable to see. I asked the tuner about it and he said the car was doing what it was supposed to; hitting 14.7 at cruise and idle and 12.5 at WOT (if i remember correctly).

My mind is everywhere at the moment so I apologize if this is all jumbled up. I am totally stumped and every person I talk to says a different thing. The best advice I think I have gotten was as follows:
-Replace the valve seals and see if that helps, and check guides while there.
-New o2 sensors (tuner said they were functioning properly though)
-Check over the PCV system
-Fuel pressure regulator? Leaky injector? (brand new also by the way)
-Pull heads and have them gone through
-Eventually pull motor if nothing is solved (probably for a re-ring)