you don't mention what type of failures you had seen (failure to eject, perhaps?) . i do know that the older model Caniks, came with very strong recoil spring assemblies, and the reason for it, they were designed to shoot NATO rounds. i was lucky to find ANYTHING as ammo during the panic crisis, and certainly no NATO rounds to be found.
when this happened to my TP9SF, i put in a call to Century Arms (the importer) and they sent me a much "softer" RSA under warranty, and the gun had no more issues.