Warping of the carb bodies over time, causing binding of the slides and galling of the bore, is common. Some blame over-tightening of the flange nuts.
I have sanded one slide twice in three years on a friend's bike, and just sanded one slide on my own bike last month. In these cases, when the carbs were removed, the nuts were not very tight at all.
For about $75 per carb, Triton will true the bore and put a brass sleeve on the slide. http://www.tritonmachining.com/
This results in perfect action and no galling, but I have not heard how permanent it is. If the carb body is really the culprit for deforming, it would seem that the problem could happen again.