Cars do use oil but the question is how much you can live with. If
between oil changes you lose a quart total, is it really worth fixing
since oil is pretty cheap, relatively speaking.
What actually worries me more is that a mechanic mentioned that there
was very little oil left: do you check your oil periodically?
I'd check your oil every fill up or more frequently, if you think you
are losing oil to get an idea how much you are using.
Useage is not a linear function in time if you don't fill it up every
time. If you don't top off your oil, It the first week you lose 100 cL,
the next week you might lose 200 mL, 400 the week after -- just
guessing at those numbers but they are just to illustrate.
Topping it off will keep the usuage around 100 cL a week.It is a lot
better for your engine, not wearing internals down.
If you are leaking oil, you could get your engine steam cleaned to see
where it might be seeping from.