R4 lock
I have had similar issues with several of my older renaults. It is a nuisance!
What you are going to face over time are worn brass pins wearing to the point where they rotate in their locating shafts. The springs will then push them into the chamber where you insert the key. They will then jam up the lock because the key cannot be inserted or turned. NO amount of ANY type of lubricant can stop that blockage.
Whatever you do you to fix this issue you will need to remove the lock and the electrical connections that piggy-back to it.
This task is achieved by removing the shroud that surrounds the lock. With the key in the ignition lock rotate the key until you can depress a brass/copper coloured plunger on the bottom of the lock barrel. It is clearly visible at the bottom of the shroud that surrounds the lock. Use a pin punch, jeweller's screwdriver, a nail, or other thin sturdy object. Use the partially inserted key to drag the assembly out.
At the same time look for the junction box that links the switch to the rest of the car's electics. Disconnect it (pull them apart). VOILA!
You now have the problem at hand and you have four choices.
OPTION 1. Buy a new lock. It is VERY expensive. Also your new key won't operate the door lock which probably works fine!
OPTION 2. Buy a second hand lock. Surely the problem won't happen again?!
OPTION 3. Undo the two long screws that hold the physical and electrical parts of the lock together. Carefully put the electrical part to one side. Remove the plastic strip that covers the pins in their locating chambers. Remove ofending pin and spring. PROBLEM SOLVED! Until, of course, the next pin erodes to send you back to do the same job. Reassembly is just the reverse. Just look out that the cross on both parts align. Sounds hard - pretty easy.
OPTION 4. Ditto, all of option 3, but remove all pins and springs. This is of course an act of bastardry. You now don't need a key! A screwdriver or any other key will now work!
Your choice!
Hope this helps you out.
David