No, but know quite a few people that have a helluva time getting those pins out. Sometimes harder than getting the barrel out, although mine wasn't bad at all. I really don't know what you could do to fix it. I've never really dealt with something like this. I know HCpookie got into alot of these types of things but I don't know when his website will be up again. If I were in your shoes and I didn't get an answer on how to replace the rear sight base, I would probably order a whole new front assembly. Luckily Tapco has got some great deals going on right now for replacement parts. You would, however,have to be a little more concerned about headspacing if you went this route. Here's the link
to the barrel and front trunnion assembly. Pretty good price for $25. Good luck with it. Maybe someone can give you some good advice without having to buy a new one. If the crack isn't that bad, and doesn't effect your gas tube fitting securely, I personally don't know if you would have a horrible problem.