I’ve had a few scopes fail for various reasons. Most of those lasted 5 or more years. Now that I’m retired and I’m shooting a lot more, I have come to appreciate Leupold scopes even more than before. I have a pair of 2-7 power Leupold that are just plain OLD, being 40 years old or more. Never had any problem with them. And yesterday I was shooting my 223, which wears a Vari-X III 4.5-14 that I bought, I guess, about 35 years ago. I sent that scope back to Leupold to have a new reticle put in it. They charged me for that, but they also refreshed the internals. Same with a 6.5-20 Leupold that’s about the same age.
So, a good scope can last a long time. That said, conversations with Leupold did make me aware that scope internals will age, though not always fail.