I found a solution. Total cost was about $20
There are two little tabs on a metal piece inside the door lock mechanism that are destined to break at some point in time. The metal they used is extremely poor quality and doesn't react to stress very well.
I did a lot of research and found out that the piece found in this kit for VW on ebay contains the same part needed for your porsche.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=320655523377&viewitem=&sspagename=STRK%3AMEWAX%3AIT
The piece you want to replace is in the bottom-right corner of the image.
Taking apart the door lock mechanism isn't as hard as it looks. By pressing down on the pole that sticks out the back, you can remove (slide out) the disc that holds everything together, getting access to the broken part inside.
I should really post some pictures, since this seems to be a common problem and paying $300 for a .10 cent part is.....unfortunate.
Since it wasn't immediately obvious how to take the thing apart, I accidentally broke the little pole that connects to the lock actuator (also cheap metal) in learning all of this. So, I replaced one .10 cent part and now I need to replace the other.
It took a little less than 2 weeks to get the part shipped from the UK. It's possible you could visit your VW dealership and find the same part available, but I'm not sure what you would ask for and I don't think it's sold separately. Your only other option is to visit a junk yard and hope they have that model of VW that carries this component.
Given the durability of this thing, I wouldn't recommend buying a used one if you can fix it yourself with a new part. The used one will certainly have a limited amount of life left in it and may not last much longer.
Let me know if you have any questions. Also, if someone has one of those little poles connected with the cotter pin, I'd be willing to buy it off ya!
-Ted