Every XLR roof has an outer skin made of a sheet-molded composite. The skin is held onto an inner magnesium alloy frame using an adhesive that appears to degrade over time, loosening that bond and allowing the skin to pull away from the frame. The majority of complaints come from 2004 and 2005 owners which suggests the degredation may not happen quickly, but it's only a matter of time befoe newer model years have the same issue.
Owners who have experienced this problem say they heard an louder-than-noraml amount of wind noise while driving, shortly before their roofs flew off into traffic.
A Roof Seperation Investigation
During a federal investigation, General Motors told the National Highway Traffic Safety Administration (NHTSA) that they believe an oxide layer on the magnesium frame reduces the effectiveness of the adhesion, but the problem takes a long time to develop.
Why NHTSA thinks the problem doesn't warrant a recall
The investigation found that most issues happened more than 10 years after the cars were manufacturered and that, along with a relatively low incident report rate, didn't warrant a recall.
Try telling that to owners.
"...while traveling at approximately 72 mph down the interstate, with the convertible top close, the top fiberglass panel of the convertible roof separated entirely and cleanly from the frame of the vehicle."
Maybe it's just me, but I find it odd that an agency tasked with the safety of our national highways doesn't think a roof suddenly detatching at 65mph is a safety concern.
So, Now What?
So an XLR's roof is likely to come off after a decade. GM admits it, NHTSA knows it, and owners are ... well, left with few options. They could have the roof reattached, but the car is out-of-warranty and the repair is expensive. Which is why some owners are just garaging their cars.
"I love the car but it has been in my garage for a year. Not sure what to do about the roof. Plan to address it this summer with a body shop. The dealer is so expensive with any kind of work they do and it's no longer under warranty."
It's possible the investigation will resurface if (when?) owners of the 2006 through 2009 model years share their own roof-flying stories.