SpareMag - have you contacted Beretta about your blued narrow slide and see what they recommend you do? I think you need to take off the slide and see if there is a crack or not. Beretta might offer a replacement for minimal fee, don't know????
I also thought I read on the Beretta forums that the wide slide versions did not take care of all the frame cracking as some were still reporting cracking with the newer versions. I don't remember what ammunition they were shooting though.