My '02 TT driver-side window doesn't seal tightly across the top at the back corner.
It does its auto up-and-down thing properly, just leaves a .25" space in the upper back corner.
Is the tracking adjustable if I can get the door panel off?

 

It's not the tracking, it's most likely the regulator (not to be confused with the motor). Sounds like it is bad. You may want to fiddle with it and yes, you must remove the door panel. Be careful when playing with it. You do not want to drop the glass and shatter it.

The regulator is wound pretty tight so you will probably have to get a new one. When I bought a new window motor on ebay, I saw several regulators...

Also try removing the window motor, adjusting the cables, then reinstalling it.