Re: the AT-84s with the special Bomar mount:
A part in the sight (the detent for the elevation adjustment) wore out and I had to send the sight back to Bomar. They noted that somebody (prior to me, actually, as I bought it used) had changed one of the mounting screws, so it was no longer under warranty. But they repaired it free -- and I had expected to pay in the first place.
Bomar has very nice people who support their products, even when someone screws with those products.
The guns shoots better than it looks and I think it looks pretty good. (Supposedly built by a big-name gunsmith [Boland] who specialized in 1911s. I have no proof of that, but many nice, custom features, including extended controls, bobbed hammer, checkering on the front/back straps, and a mag well. Wonderful trigger in both SA and DA.) I had to replace the front sight when it died, too, and that was harder, as its staked with a funny Millett-type set of posts. It also had some strange custom contraption with an insertable tritium element. Just went with a plain blade on the replacement.
(The slide was originally parkerized, but I had it nickel-plated by Jack Fuselier in Texas. Fitting the refinished slide to the frame was a task, as the slide to frame fit on this gun was very tight to start with...)