I was the third or fourth owner of a Ruger pistol. I sent it to them for work and they sent me back a "Tack Driver". The invoice included said, "No charge, Warranty Work".I have never heard of Ruger refusing to perform a repair on any of their arms.
Well, any arms that are in current production.
Likewise, outside of owner modification, I have never heard of them charging for a repair.
I called S&W to order some parts for my second hand pistol. I lost the part. I was told the part was coming under warranty and a batch of other parts were included for no charge. The guy laughed when I asked him if he needed my CC.
I can't speak for all gun manufacturers, but my experiences above are good ones.