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If you weren't burning that much before with petroleum oil, try switching back and see if your consumption goes back down.
I'd guess that your piston rings are probably worn and that could be diagnosed by using a cylinder leak down tester but not all techs, shops have one. I have one and it's about a $200 tool sold by Snap-on but by presurizing and measuring percentage of cylinder leakage, and if low, one then adds oil to a cylinder to see if it improves and if so, your rings are the cause.
A compression test (both dry, then "wet" with oil added) might lead to the same conclusion but the leak down test can help pinpoint exactly where the compression is leaking by listening for escaped air (like rings or valves). Bad valves or valve guide seals wouldn't cause that much oil consumption.
Another possibility with a turbo engine is that your turbocharger could also be the cause, either front or rear turbo seals could be leaking and you can't see that on the outside. If it's a rear turbo seal, you can usually see that by removing the front exhaust pipe and the backside of the turbo would be very oily on the inside. There's always some oil mist "blowby" on the inside of the front seal to intercooler hose area but if you remove the intercooler hose from the turbo and see ALOT of oil, then the front seal could be your problem as well.
Before spending cash on trying to have it diagnosed, try simply switching back to "normal" petroleum based 10w30 first and see if that helps. It's generally not advised to switch to synthetics on high mileage engines.
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