Originally Posted by Proby
From what, just poor assembly?
Older windows just didn't have the technology or methodology. When replacement windows first came out there was a plethora of companies that came to the market to fill the "upgrade" market. Many were flashes in the proverbial pan and disappeared. Others were diligent but lacked the expertise to make a sustenable product. Some built a product whose lifespan is at an end.
I don't know which category the poster falls into, but I would guess this is the first of a series of failures in his windows.
Aluminum windows and metal windows in general are older technology. That's why I thought the posters windows were 70's-80's vintage.