Audi A5 2.0T oil issue repair - out of warranty

Looking for some advice please, I have two questions below about my A5 and oil consumption. I know this is an old and repeated problem for the 2.0T, so I'm not looking to confirm that the engine is an oil guzzler / the old piston ring problem.

Background (sorry it's a bit long): it's a 58 plate 2.0T petrol model, (FASH, and 67k miles). I bought privately and it has no warranty. It's burning too much oil, much more than 0.5l per 600 miles (1000km) specified in the handbook.

So far an independent specialist garage has changed what they called the oil separator for £150 as he said it was being mixed in and burnt off. Straight after the repair it was showing max oil on the MMI, and held that position for 200 miles. It's now suddenly halfway between min and max on the MMI, which I understand represents not total engine oil (4.7l), but the top most litre in the engine meaning it has burnt 0.5l in 200 miles. I also bought a manual dipstick to check and confirmed.

Questions are:

1) Have people experienced such a drop in engine oil after a repair in around 200-300 miles? I saw on another forum that after such a repair it can need a little oil to work into the engine, to compensate for the fact it was previously just being burned off.

2) If my piston rings are knackered (as I fear), what are my chances of pushing audi uk to support with the cost of the £4-5k bill, on the basis this is clearly a manufacturer problem, and not general wear and tear.

Thanks