Answer

VW mechanics joke that the factory hangs a heater core on a wire and builds a car around it.

 

You'll need to evacuate the A/C system (if you have it). Once you have the dash out and are looking at the heater/evaporator case you'll see that there are actually two cases that are clipped together in the center with a vertical joint. You can try to separate the heater case from the A/C evap case in the car, or you can simply remove the entire assembly and split it on the bench. I prefer the bench.

 

If you wish to separate in the car you need a mirror, a flat-tip screwdriver assortment, and patience befitting a saint. You'll see there are at least two spring clips on the bottom side, three on the front firewall side, two or three across the top, and three or so on the side facing the passenger compartment. Once you have these off, and have disconnected the heater hoses, look on the engine side of the firewall under the metallized heat shield and you should find some additonal flange nuts. There should be at least two, maybe as many as four. Once you have these removed you should be able to muscle that bad boy out of there. I charge 11 labor hours to perform this job in my shop. Lots of customers run screaming from this price, but lots of mechanics run screaming from this work. Good luck.