What’s the life expectancy of skylights?

Skylights are beautiful things because they improve the atmosphere of interior spaces so much. They should also keep out water indefinitely. That said, many skylights are not designed nor installed to live up to this potential. It sounds like this is the cause of your problem. I’ve made it my business to monitor skylight technology over the last 20 years, and I have yet to see any brand that’s technically better than Velux (800-888-3589). The company founder, Villum Kann Rasmussen, invented skylights in the early 1940s, and this family firm still makes the best products I’ve seen. Contacting the company directly is the easiest way to get reliable replacements for what you’ve got now. Velux offers a trained installation workforce that know what they’re doing. Also, depending on where your replacement skylights will be located in the house, consider openable units. It’s amazing how much summertime ventilation within the entire house is improved when hot air is allowed to escape upwards, out through the roof. The difference is often enough to make air conditioning unnecessary on days you’d normally require it.