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The seal just glues on to the perimeter of the body,the sunroof slides up to it. But why is it bad? If it is because of water leaks,this is caused by the drains in each corner being plugged

The seal doesn't really seal it from water leaks. If you open up the roof and look in each corner you will see a drain. They get filled up with "stuff" and need to be cleared out
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derf
No matter where you go,there you are.
My post are my opinion of what has worked for me but are not the gospel

What I post is what I do on my cars. I am here to try and help not to impress or boast