Bootmachine... I had the same thing happen twice with my FF.. You need to replace the Y shaped spider gear yoke with the upgraded version... Better and thicker steel.. I haven't broken one since... If you took your diff apart for any type of cleaning you may have forgotten to reshim the gears.. This is critical to the longevity of the diff... I doubt the gears were put in worng because they won't fit... Unfortunately, you also broke the bevel gear which is sort of expensive.. when mine broke, it took out the diff itself, stripped the bevel gear and also, knocked a hole in the front diff housing... pretty cool but ended my bashing on vacation on Marthas Vinyard last summer.....