service@pitbullguitars.com should get a response. But they are a small part-time outfit, they don't go in to the warehouse every day of the week and with it being summer holiday time, it may take a little longer for them to respond than normal.

A good neck should start off flat and shouldn't really need a dual action truss rod, but it does allow some correction when less than ideal wood is used for the neck and from what I've read, a dual-action truss rod is a bit stiffer than a single-action one, so makes the neck a bit stronger.

Without having the neck in my hands, it's hard to say whether you've reached the truss rod's limits or not. It may be hard to adjust simply because the neck doesn't want to straighten. There should be that very loose middle section, and then you'll have a reasonably firm portion, and then at the end of the adjustment it will get very stiff. I'd wind the truss rod clockwise until you get that slack section, then keep going until it bites and you start to increase the amount of convex back-bow. Then wind it anti-clockwise again just to see if anything changes. If the truss rod gets really stiff, then don't go any further as threads are likely to snap.

I don't think it's possible to get the nut off a dual action rod to grease the threads the same way you can a single action rod.

If the neck's twisted by 3-4mm, it will need replacing anyway. A lot of necks have a very gentle twist, some of which can be compensated for by fret profiling, but only for very gentle twists. Anything like 3-4mm and the action will have to be very high (basically unplayable) to stop notes choking when bending them.

The neck joint shouldn't be very loose. They are normally a reasonably tight fit, and you can sometimes put the neck in the pocket and it stays where placed. Others I've had were still pretty firm. There shouldn't be a 1mm+ gap in the neck joint area, though a lot of the base of heel to base of pocket joins aren't particularly even.

It's all jigs, templates and routers for these kits (and some of the templates leave a lot to be desired). CNC machining would be nice but you don't get it with these kits.

I don't know how true it is now, but when Trevor Wilkinson was setting up manufacturing for the Vintage brand of guitars in China, he despaired at getting good quality control and basic manufacture from the factories he tried. The workers were young and unskilled, teenagers to mid 20s, after which time then normally moved on to other factories and other jobs. You need to be able to install your own quality control and training on dedicated production lines to ensure a consistent product and for the number of kits that Pit Bull sell a year, plus the multi-factory issue where you'd need your own QA man in each one, it's never going to happen, so you are reliant on what the factories provide.

100% agree on lack of care taken for the veneering process. But once the glue's dried, it looks good so it gets shipped, and never mind the poor person who has all the issues when trying to stain it.