Mine went the other month.... heres how i fixed it....
Tried getting in the boot and removing the trim which was a pain so i opened the key slot slightly with a screw driver and blasted loads of WD40 in there and worked the key in and out, after a while of locking/unlocking the car it finally worked.
Once opened i removed the trim and gave it a good covering with the good old WD40 and not had a problem since