Although I haven't explored the availability of parts for the Gas Gas 2-stroke starters with them, Stockers Starters has been a great resource for me in the past.
www.stockers.com
In addition to yamaha street bike and atv starters and Polaris starters, I was able to get all the replacement parts needed (including the square bodied sealing o-rings) to do repairs on my 2004 FSE 400.
Thank you for taking the time to document your experience and findings as you worked through your starter difficulties.
I'm still relatively new to the GG 2-stroke electric starter experience, but I can tell that my starter has some friction and slop with the bendix action. It works very well, as long as it's not too cold, so far, but I can see it acting up before too long. Thanks to this thread, I have a much better understanding of my starter, and what will need to make it work smoothly and for a long time.
Good Ridiing and Wrenching to You All!
Jim