I own a 1999 323i and the interior windows/glass of the car fogs up
something awful.  Far worse than one would think to be 'normal'.
The defrost, particularly in winter or when raining (I live in
Massachusetts) cannot even do an adequate job of keeping the windows
totally clear.  I have not had it checked out, but I believe it began
after I had the windshield replaced a few years back, though I cannot
be totally certain.  (I can also mention that the headlight lamps also
fog up some though I find it difficult to believe that this is
connected.)  It only has 30K miles and I plan to sell it, but would
like this problem fixed first.  Still, don't feel like bringing it to
BMW dealer or repair unless I have some insight to what the problem
might be.  Any thoughts/suggestions would be appreciated.  Thanks.