So to follow up on this post. This situation just got worse by the day. No it wasn't a genuine part, my mistake.
Anyway, a friend of my daughter put me on to this video on youtoob 
https://www.youtube.com/watch?v=izr2tYdf9co
Which lead to this video 
https://www.youtube.com/watch?v=Fk_vwrZCjb8
So on Saturday I tried the first option but could not get screw drivers in there and to be honest couldn't really see in there adequately. What I did see though was the cable from the inner door handle come off when actuator slipped down in side the door. You know what that meant. Yep, pull the door apart again. I've become quite good at this now.
Once I had retrieved the actuator from the door I looked closely at the mechanism in question (see videos) and the piece that required bending was not in contact with the plastic piece at all. Not even sure it is supposed to be. However, I bent it to make contact and applied some white lithium grease to aid in any friction issues that may arise. 
Before reinstalling I sat with the actuator a screw driver and the key for some time activating the lock (as if the door had been closed) then locking with the key. Unlocking with key then activating actuator to simulate opening the door. Over and over and over with no negative issues. 
At various stages of reassembly I continued to test and retest to ensure this was working as it should, again, without any issues.
The door has now been opened and closed on numerous occasions (normally without the need to slam it) and locking and unlocking has been normal.
So, before you splurge on a new door latch maybe give this ago. I'll report back later on how this is going.
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