Here's what I found today on my antenna base. No corrosion anywhere, a good thing of course, but kind of strange considering this car spent most of it's previous life outside.
The arrow indicates flattened coax.

As a ham radio guy I know that's a bad thing. I thought something was wrong when I tried to pull on the coax coming out of the threaded base and it wouldn't move. Either someone had already replaced the base and caused this problem when tightening the crossmember screws, or it came this way from the factory. Regardless, the coax was pinched between the silver crossmember and the body.
Also, that tan board on the right is what resides in the black plastic antenna base. It's actually a circuit board with some electronics on it. You're seeing the back of it in this picture. When mounted on the car, this is outside, covered by the black plastic thing that the antenna mast screws in to.
Now perhaps I know why VCDS would occasionally show "antenna - short to ground - intermittent".
For anyone that has to replace it, on an '03 Golf it is moderately easy, but the PITA meter is almost pegged. Because you'll never want to do this again, buy this part from the dealer. 1j0-035-501-f, $85 at MIG. Chinese Replacement Auto Parts (aka crap) well, sometimes there's a reason they're cheap. That was not the case with my problem, but I didn't want to find myself missing a gasket or something cheap (but absolutely necessary) that would have come with an OE unit.
