Sandpaper, needle files, and a little more care and attention to detail than you got from the folks that built it, and yer good. Make the notches a little deeper, scuff a bit off the side of the latch, touch up as required. Take off a bunch of sharp edges while you are at it.
The latch on the one I have is very stiff, as was the barrel nut. Cannot recall having to muck with the nut retainer, so mine must have worked well enough.
My main solution was to live with it, and only take it down when I need to, for the most part. Takes a minute or less of fiddling with the nut to get it 'right', then it's back to the show. I suppose I could put some thread locker on it, but...
Mine has a Browning extractor in it, as it lost a claw on the original, a long while back. The Browning unit was available, and dropped right in.
For the price, think of them as a kit. The reason they are assembled and sent out, is that it is the easiest way to make sure you have all the parts. Stripping it down and having a go through is pretty close to a requirement. YMMV.

But that's how I see it.
Cheers
Trev