It's not just cleaning, it's cleaning and lubricating. The original grease getting dirty and drying out is the problem.
Here's the post referencing a DIY article on a VW forum:
Squeel on start-up
This will help with working on the starter itself only. For removal instructions you'll need the Bentley manual, pages 27-8 & 27-9. I've heard it's PITA. A project I'm not looking forward to.