#1 the new vw's really have no place to snap in tabs, so the sleeve wants to pull out an inch each time,
You probably need to get a proper DIN mounting kit from Crutchfield or a car stereo dealership. There is a screw hole in the back center of the sleeve that can help mount stuff to kits like that.
In my case (not on a VW), I drilled holes in the sleeve and screwed the sleeve to the dash frame.
the mempeg doesn't look like it covers teh sleeve well, so you see the metal sleve on 3 sides of it.
This might be solved by a proper dash kit from a car stereo dealership. These sorts of things usually crop up when you just try to "stick the stereo in the hole".
However, I also could see some air around the sleeve on my Honda installation. So I took a piece of black plastic and cut a rectangular trim shape out of it, then glued that to the front edge of the sleeve. Now it looks perfect.
Pics of my Mk1 install (including sleeve trim and side screws) are available at my web site -- click on my name at the bottom of this message. Although I now own a Mk2 for which I have no pictures, it used the same technique and looks similar.
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Tony Fabris