Their response stating that they replaced the frame due to it being cracked seems like a well crafted corporate answer, designed to protect themselves. I can understand that. With that said, the fact is that they are taking back a product and replacing a frame that is likely 30 years old at their expense. Not many commercial companies would be willing to do that, especially considering it could have been owned by multiple people and who knows what it's service life has been.
It is hard to complain about their customer service as I have found Glock to be an outstanding company when it comes to how they treat people. I understand about the finger grooves. For some the work, and others they don't but it is not a hard fix and there are a bunch of tutorials online about how to eliminate/modify them to a person's liking. I smoothed the finger grooves down on my old G19.3 years ago and while it may not look perfect it is certainly functional, which is what I care about, as I view them as a very high quality practical tool.