Definitely bellhousing then, one of three in locations 4, 6 & 7 in your original diagram. That implies the gearbox has been off at some point, possibly for a clutch? Maybe the bolt wasn't tightened fully and managed to escape. Its surprising it went forwards actually. I would have thought it would have fallen out the back.
I wouldn't worry about the missing one tbh. Not all implementations of the 01E gearbox have a bolt there anyway, plus the special S8 version is NLA anyway. Its possible to fabricobble one if it bothers you, but I'd just ignore it
The other implementation of a bolt of that design is an M10. Many internet points to anyone who knows where it is
