On turbo models it may be signs off turbo oil seals on the way out. If its burning very little it will be hard to notice the loss of oil. Another common thing is the sump plug and washer. The cars have ally sumps and are very easily crossed threaded, this would let oil weep out.
Other than that could be valve stem oil seals, piston oil seals letting abit of oil past and into combustion chamber, very heavy breathing engine.