As long as when you ran your engine in with mineral oil and then afterwards change to synthetic oil I donnot think your engine under normal circumstances is using this much oil from my expierence unless something else is creating this.

my saphire stage 2 was even after complete rebuild still using oil due to not a good breather system ( open vent ) ... and a friend of mine on his stage 1 is putting so much oil in we even wonder if service is needed yearly ...

But my standard 3 door now is not using any as far as I know ( should not say this to loud ... )

As long as your engine is running OK and set up correctly do you want to opne up the car again and not find anything with that money you can buy some liters of oil to run it anyhow , just make sure you keep checking on a regarly base.

Steven