Agree that asking for the parts is the best and my 'new' Nikon 8x42 HG LX has been the closest to perfect from the start, but I did notice how easily the eyecup rubbers were to take off, in my case just for repositioning.
Interesting topic because like most things now it could now be considered too 'expensive' to set up the facilities to do anything, even if that could be feasible at all, and it's ironic that perhaps the expense would mainly be for installing the computer programmes and the departments to handle the admin! Also I wonder if there are many engineers available who can really do any repairs.
I usually get them second hand and when occasionally things weren't right I have guessed that original owners did not want the hassle of trying to exercise the 'warranties', so sold them to me instead!
Apart from rubber, the uncorrectable defects might perhaps include any to do with collimation, which the original owners/suppliers could certainly have been expected to mention so they would have been unacceptable. This could also be claimed by mfg's as 'damage resulting from misuse', i.e. dropping the binoculars, but I think this is a bit dubious because this is bound to happen, but has caused no problems so far :t:
The main things have indeed been excessive focussing play, presumably due to the quality of the parts themselves, rather than by the process of hand assembly. Even with such relatively expensive hand made items, in this respect I can only suppose there might still be 'friday night' examples. When they were new, at Q.C. it might even have been quite hard to tell how much play were really there, and then exactly where to draw the line.
In my experience Bushnell UK just made things worse and ended up with replacement, but after a huge hassle. Cley Spy checked the play in my (Vanguard?) and said 'they are all like that' so accepted the return. Vortex replaced Fury 6.5x32 free of postage to USA, and Meopta replaced 12x50 HD case, and then the binoculars themselves (but still a bit of play), f.o.c.
With the latest, a Zeiss 8x42 Victory FL, it has just had 'to go through a Zeiss dealer', which added another layer of admin, and I am waiting to see what the answer to excessive play might eventually be...wish the Zeiss problem had just been with its rubber eyecups!