I'm so glad I found this thread!
I have March 2009 unit, part number 1T0 035 680 C, HW: H04, SW: 2680 (from the label on the unit).
Many years ago I updated the firmware, to which version I can't remember and it's worked fine ever since.
Yesterday I tried to update to 5238 by Josi, the update seemed to go through fine other than I had no sound and the radio stations all saved to the presets as 93.4mhz no matter what station it thought I'd tuned (I had no sound so took for granted the station name that was showed was the station name that should have saved to the preset). The navigation worked but I literally had no sound at all.
I've tried various different versions today including 4120 and 5218 which both showed a SWL ERROR and finally managed to install 3810 (from the original post on this thread) and the sound has returned.
Could anyone tell me which version(s) will work on my unit and is it actually worth upgrading from 3810?
Many thanks to the original poster for the links and thanks in advance to anyone who can answer my question.
Nick.