A My A6 c7 has came up on the dash to add 1 litre of oil. I added 1 litre and then came up again 1 week later, done the same again. Eventually I got the mechanic to check it out. Couldn't see anything wrong , no oil leaking , replaced the engine oil sensor, 5 litres taken out and 7 added. Three weeks later same thing happened again. Dip stick added and the levels are okay. Anyone else experience this or similar? Thanks