You might be able to squirt some sealant under the area that is leaking, I've done that before but don't like to do it as some excess glop always shows up on the paint. Finding the leak is no fun too.

Incidentally, you may have a hard time finding someone that will sign up to reuse your glass, unless it is on a best efforts basis, meaning if the glass breaks they aren't responsible. They like to use their own glass supplier as they make a profit from that. They get the glass for say $75 and sell it to you for $150 plus labor. Its a high markup and I've played one glass shop against another before.

There are fewer experienced installers for the roped on glass like these. On the new cars they just slap the glass on with some RTV under it, the time and skill required is nothing compared to the old windowglass.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!