Driveability problems relating to low oil would be blue smoke, loss of power, and/or unusual engine noises.

Leaks can best be detected by checking the concrete under where you park - if you are unsure if the oil is new there, you can spread newspaper, leave it overnight, and see if anything shows up. Any oil that leaks out will find its way to the ground.

I am with MD, that kind of oil usage is absolutely nothing to worry about. You also don't know where they filled it to, you haven't necessarily used 3/4 litre of oil, as they may have filled it to the half way point.

Check it and see what the consumption is by monitoring the oil level over time (every few tankfuls) but don't get too worried by it.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue