Having tried numerous brands of SLR (film) in the past decades, I've had used 奸郎 SLR for about 10 years (starting with AE-1). Then switched to their DSLR for yet another 10 years+. I would say, their QC (especially since the switching from film to digital) were always no good. The L glass QC was the worst area in particular.
Long story short (not to repeat my bad experience in details), QC was one of the main reasons that made users (at least I am one of those ...) switching to other brands (mostly to N).