I haven't run the numbers lately, but back in the day the rule of thumb was that as long as you didn't burn/leak more than a quart every 1,000 miles, you were golden. Even then, save for trivial leaks, the cost of repair vs the cost of oil made action to repair un-economical until you got down around a quart every 300 miles or so.
In any case, the point is well taken: it is never too early to pay attention to things around you, like fluid levels for your car . . . some of those things can kill you, some only cost big buck$.
'12 X5 35d
'05 Jeep Libby CRD (now deceased)
'01 VW Jetta TDI
formerly '69 BMW 2002 and '67 BMW 2000CS