The reason some of the rets broke was usually because they were on harsh shooting springers, I remember the Sniper model with graduated ret which was etched, a nice scope for its day, also the Beta 3s which had level built into the bottom of the lens

I spoke to Paul Kassnar a few years ago, I dont know if hes still around as he was pretty old then, he was very pleased to get some good feedback on those old scopes, made in Japan and certainly one of the first really useable optics available for air rifles