Just because a bike uses oil doesn’t necessarily mean that it has a problem. For a long time now, bike makers have designed engines with under piston oil feeds.
These are there to cool down the piston crown so that the engine can reliably produce more power. However, just like petrol, engine oil will evaporate at certain temperatures, and it gets pretty hot under pistons doing 14,000 revs a minute, so the consumption can mount up, especially if you use the bike hard.
A race bike at the TT can get through half its oil in six laps, so manufacturers quote maximum oil consumption figures of one litre per thousand miles.
As long as there is no evidence of oil burning at the exhaust end can, and you get into the habit of checking the oil level before you go out for your next ride, there shouldn’t be a problem.