I spoke with Nissan yesterday afternoon about my "AntiVibration lockscrew".
Exactly inline with amts's comment they will not weld the nut back on as it will weaken the receiver.
As the towing kit is supplied by another company and they have had a few cases exactly the same they are considering replacing the whole towing kit with a new model that has the lockscrew welded in properly.
Using the tow bar without the antivibration screw is OK in the short term, it will just be noisy when the weight comes off the bar.
Thanks to Tim at lakeside for following this up for me with Tech Line.
Ill post back here when i have a result
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Current - '08 T31 Platinum TL Diesel Manual
Mats, Boot Liner, Roofies, Spotties, Tint, Nudgebar, Tow Kit, Bash Plate, Yoko GO12 AT-S, Forum stickers.HiTech Twins, LED Mirrors, Bonnet Protector, LED steps
Old - '04 T30 Ti-L Auto
X-966