I believe my query is more something for a gunsmith rather than a lever action rifle user. Gunsmiths should have more opportunities to work on rifles about which I query than most rifle owners. Comparing [better] modern push feed bolt actions' long term reliability with circa 1950s Savage Model 99s having side lever safety and chambered for 243/308/358 cartridge family, how well does the 99 match-up? There were nearly one million Savage Model 99 rifles having side lever safeties, and just under a hundred thousand of the 243/308/358 cartridge family with such safeties. I doubt hunting rifles, as a class, are fired a thousand times during an average deer hunter's hunting career. So a sixty-year-old Savage probably is at no disadvantage in long term reliability other than it might need a barrel somewhat sooner than a newer push feed bolt gun.