Zeus, Sorry to hear of your problem with the high oil consumption, and the gauntlet you are experiencing. The problem seems to stem from the the wrong type of oil (Dino), used at those 10000 mile extended intervals.
Since having changed to synthetic oils, and if you wish to continue using them, I would go to Mobil 1 Delvac in a 5W-40 weight, for it's cleaning effect. It is very high in detergents and anti-corrosive additives, to meet the Heavy Duty Diesel Req'ts. for that purpose. It can be also used in spark ignition engines-gasoline, as it is formulated for that use also. I would try this before tearing into the engine or selling it.
I would use the Dino version of Mobil Delvac 15W-40 $8-9./gal., and add Marvel Mystery Oil to the engine oil and to the fuel. Buy a 1 gal. jug of MMO, at Wmart for about $12.50, and use it as directed for mixing with the oil and fuel. It will turn the oil black pretty quick, and you may want to change it at 1000-2000 mile intervals, with a new oil filter. Add the Dino 15W-40, as needed for topping up. Do this several times before you give up on it. MMO is used in the USAF by 55gal. drums in older non-turbine engines. Gen. Aviaton too.
If all this doesn't solve the problem, I would use Dino HDEO's like Mobil Delvac Super 1300 or Shell Rotella, Chevron DELO, etc., and keep the oil consumption to more reasonable levels. Oil consumption or use is not bad for an engine, it's bad for emissions and the wallet.
Don't tear the engine down, if you can reduce the oil consumption, by whatever means you can find that will help reduce or stop it. Good Luck.