I was having difficulty inserting the key in my (north-facing)
eurolock and sprayed the keyhole with silicone-based lubricant.

The key now certainly goes in and out as it should, but it can turn
without actually locking the door. Turning it with the door open does
the trick and the subsequent try to lock the door locks it. It unlocks
with no problem, but can't help worrying if it's only a matter of time
until I lock myself out of the house or until I am unable to lock.

Is the lock on its last legs or have I caused temporary illness to it?

Thanks,

Kostas