Sticky Euro cylinder lock
Far from being an expert, here is my personal experience: silicon dry spray alone inside the cylinder, and  WD40 on the sliding mechanism.

As for the cylinder, I had been advised to use  graphite dust or silicon dry spray (non-greasy) by different key makers. I first used graphite dust, but it tended to agglomerate, so I finally used air duster cleaning to remove graphite dust and grease employed by former owners, during a hot day so that the old graphite &amp; grease mix was liquid enough to pour out of the lock.

One important lesson I learned to never leave keys plugged inside the lock, because it prematurely ages the mechanisms.

Additional source: LocksOnline : help  maintain  locks