That's a bugger. If you know the size of it you may be able to source one through a local MB dealer or a specialist bolt store. I've sourced parts through 3 Point Mercedes at Mount Gravatt and also through Boltmasters in Morningside.
I imagine you now also have to get that bolt out? Might be worth dropping into a MB place who should have dealt with that issue previously.
And lastly, I know you've heard it before as you were part of the discussion, but it's worth flushing the trans cooler as well when you do the fluid. Last couple of pages of this thread is where that discussion took place.
http://www.ausjeepoffroad.com/forum/...d.php?t=152993