Yes, it didn't seem loose but obviously something is wrong with it, maybe dissimilar metals with electricity going through has caused contact corrosion (poor choice of plating on connector?).
Now my diagnostic socket no longer works (cannot connect to any module) Unfortunately the wires to it were peeping out and got singed and were stuck together so will need to sort that out today.
To crimp it harder I would need one of these babies...
https://www.youtube.com/watch?v=4r-88796Bls
£1200 for cheapo chinese one and £3500 for a European one
https://www.ebay.co.uk/itm/6-Ton-Bat...r/301834375633