When I asked the Irish Snipers at the International Sniper Competition at Fort Moore about what they did with their own AI Arctic Warfares, they flat out said, "...they never break."
They've had the same bolt assemblies, the same firing pins, even the original barrels, on their rifles, for almost 30 years. And after all this time, they're still competitive. It absolutely blew my mind hearing this.
I honestly had the same question for them, about what breaks and what you should have parts for, which is how I learned of this. That said, I don't think I've seen or heard of any AI AT308 or AW breaking.
I'm all ears for counter responses and examples of anything breaking and needing replacement though.
Update: this very much reflects using .308 exclusively. As
@taliv has pointed out below.