They don't NEED to be fixed at all, these are battle rifles not precision target rifles and the play between the upper and lower does not affect function or accuracy at all. As soon as people get it out of their heads that just because it costs more than $2000 it should be some kind of sub moa semi auto target rifle the sooner people can just be happy with their rifles and get out shooting instead of coming on here whining about the cost of black rifles in Canada.
The reason the tolerances are loose on a battle rifle is because they need to make them reliable and the rifle is built loose so it will continue to function when it has some crud in the action, if they were built to tight tolerances the rifle would only function in the hands of civilians because all we do is drive to the range or our favorite shooting spot, take the rifle out of it's nice protective case, shoot 200 rounds through it then take it home and clean it. Try running around for a week with it quadding and fishing, drop it in the mud a couple times (check your bore is clear before firing), shoot 1500 rounds through it between cleanings and guess what, that's right it will still be functioning, try that with a tight tolerance semi and you'll be stripping it down to clean it out so it will function again.
I do agree that the Famae are overpriced but it isn't because there is some play between the upper and lower.