I work at the Norwegian national Hasselblad distributor, and between us 500-series geeks here at work there's a well-known fact that A12 backs have a tendancy to have lightleaks. I myself own three backs, a C12 (which I have used quite a bit, and not experienced any misfortune with) as well as an A16 back and a A16 "Super Slide" back which I will probably never use for anything.