If you dont have one and have only shot one, once upon a time, and saw it in a "movie" , I doubt you have a handle on just how sought after these little gems are. I've had one for years and the only repairs have been the std consumables, extractor, barrel ratchet lock, recoil springs ect. I built a can for mine and it is the icing on the cake, Perrazi's experience rivals mine, accurately.
The Swede K gun was built just a well as it needed to be, the 76 is a very well built piece, the machining isnt evident externally, but it is if you look inside, fouling cuts in the tube for one, S&W magazines are well made and expensive, The modified Swedes, Port Said, and Suomi M31 mags work with minor fitting and a tenth of the price.
As for the mp5 and macs, I have drawers full of dead parts, pounded uppers and lowers cracked, bolts and trigger housing split and cracked bolt carriers. Ever try to replace fire control parts in a K gun and you will wish it was a 76, Mp5s that quit take a lot more than a quick roller change to get them reliable again I built up a quick change barrel assy just to keep them running with out the special barrel press and hit and miss bolt gap setting.
All sub guns need tender care, and most owners do not have the armorers skills and tools to do what is required to keep up with Heavy use. The average NFA owner probably wont wear one out using it,
they are not in-expensive in the ammo dept.
Sorry rant over, one of you struck a nerve......