I've had scopes that needed work on two occasions.
Once it was a Leupold. Took it back to Williams' Arms, where I had bought it used, and they sent it in for me. Took a few weeks, came back good as new, cost me about 10 bucks for shipping/handling/etc.
The other occasion was a Bushnell, a cheapie 3-9x AO airgun/rimfire model that cost less than $100 several years previously. The adjustable objective went haywire. Bushnell has (or at least had at that time...6 or 7 years ago) a repair outlet in Scarborough. Took it in to them in person, explained my problem, watched the guy take it into the back room, and within 60 seconds was handed a brand-new, slightly-upgraded version of the same scope. I was happy as a clam.
In neither instance was I asked for a receipt, warranty registration card, or anything else. Good thing, cause I didn't have any.
For a serious hunting trip, I just feel better with a Leupold on my gun. For the vast majority of my guns, shooting casually, just for fun, Bushnell fills the bill nicely.
John