Chainsaw Repair

Hello.
New to the forum.
I have a lightly used 235 (2008).  It was having some running issues so I cleaned up the carb and reinstallled.  Nothing changed.  Bought a new carb.  Much harder to start.  Put original back on and swapped to a new coil.  No changes.  Noticed a lot of oil in muffler.  Replaced cylinder and piston.  No change.

I have a friend who is a small engine guy for about 10 years.  He has done over 200 chainsaws.  He is ready to give up on this(has about 4 hours into it; I have 1 hour doing the first carb.

Symptoms:  Will start fairly easily, runs well between 10-20 seconds, then shuts down.  It has done this through the numerous teardowns.
If you hold the throttle wide open, I will continue to run, but shutdowns after letting off throttle.
He has adjusted the jets numerous times, from factory to quite a more and/or less; no changes.

My friend doesn't like to lose, but we are out of ideas.  My 435 will fire up even after for sitting over a year.  This 235 is driving us nuts.
Any ideas would be appreciated.

Thanks
jeff

Thanks for the reply.
No, no pressure test, but my guy said he was thinking it might be crank seals and wasn't worth repairing.
jeff