Oiling locks
A locksmith told me never to use WD 40 in locks because, when it dries, it leaves a hard residue that when subsequently lubricated can become quite abrasive and wear the mechanism away....and without lubrication can lock the lock solid (eh!)
A blob of engine oil is better 'cos it doesn't dry and leave residue and clings to the lock mechanism better, giving better lubrication.
So perhaps penetrating oil has made your lock worse?
Fill the barrel with engine oil - well at least a few drops and work it in by turning the key. Even warm the lock up with some hot water first to flush out the WD and help the enging oil get into all the nooks and crannies.
Should work a treat.
If it doesn't I expect you'll let the whole world know.
Kevin