You can get a new lock or you can fix it. If you follow the link above (this one) DIY:
VW Golf MKV/MK5 door locked/stuck - FIX!!

Look at the photos and the 7th and 8th pics show two red plastic parts attached to a steel part there is a round spring there about the size of a 10cent. Try just removing the spring and see if the lock works again. Mine has been faultless since I did that. That was after dismantling the entire lock and the micro switches to find nothing wrong with any component. The locked worked but not all the time. after removing the spring (which just seems to add load) it has worked every time.