Same thing happened to me too..
Took it all apart, cleaned it, lubricated it and mounted it back on.
No difference.
So, took it apart again and carefully observed the locking function on the lock assembly. Discovered a slight wear, so i decided to give it a few solid knocks with the hammer on keypoints to even out the wear, and after that I grinded the sharp edges with a file to make it work smoothely. I advice you to bring the lockingassembly out of the car and into your garage or workshop to perform this properly as you need good light conditions.
I also drilled up the connection arm between the solenoid and the motor resulting the connection arm pushing the locking assembly a litle further
Worked like a charm, however I am not sure if the drilling really was required. Saved me some bucks, did not exchange any parts at all.
On reassembly make sure that you dont push the locking nob too far down, this will make it jam and keep you busy for a while:)