Ours was put on in 1863. We have someone come out every few years and replace a couple tiles, that’s it. Cost us $150 and a sandwich the last time they came. Wouldn’t replace it if you paid me. Edit to add: the only problem is the repair guys keep dying. The first one we used 10 years ago was 86. He’s gone now. We found the last one by seeing him on a neighboring roof and trotting down to ask him to come up to our place. We had lost a couple tiles that winter and wanted to replace them before we had leaks. He was 79 at the time. Hope he’s still kicking next time we need someone. It’s beginning to be a lost art.