A g/box breaking can hardly be described as an act of god.
I suggest you re-read my reply, which covered the possibilities you point
out.

What I disagree with is your statement that even though the damage occured
when the car was in the garages possession, "they have no liability". Which
is simply not true.
'Maybe' they haven't, but without more information about how it was treated
whilst in the garages care, the possibility that the garage 'were' directly
responsible for the damage occuring at the time it did, can't be ruled out.

As I see it, it's up to the garage to prove it wasn't their fault, rather
than for the owner to prove it was, and the only way I can see to do that
with any degree of certainty is for the g/box to be checked to see exactly
what is wrong with it.

Speaking as an engineer, it's often possible in the case of breakages to see
signs that a component was previously cracked, and ready to break at any
time.
If that were the case with the OP's g/box, it would let the garage off the
hook.
Just one example of how a check of the g/box could help in establishing if
anyone in particular could be held responsible for it's failure.

I don't see any point in the rest of your reply  We could all speculate how
the damage actually occured but that is irrelevant to the point I am making.
The point is whether it was caused by the garages negligence, or whether it
was a weakness in the g/box, that was ready to fail at any time.
Mike.

Well, there's a happy ending to the story. I did take it to another
shop, the one that quoted $2500, and they were pretty useless and left
the linkage disconnected after two hours.

Teetering on the brink of pulling the plug on my Terry Schaivo of a
car, I followed the advice earlier in the thread and checked out
bimrs.org. Turns out I remembered one of the shops nearby was where the
previous owner took the car, and that he highly recommended them. So I
had it towed to this third shop, praying that the instrument cluster
parts from the first shop and the tranny linkage parts from the second
shop would follow along with this unsupervised tow. (Checking for a
joyride is hard with the cluster in North Carolina!)

Turns out, this was a stroke of luck. Grant at Alexandria Bavarian
Motor Service http://www.alexandriabavarian.com/ knows his stuff
backwards and forwards, and they were able to fix it in 20 minutes, he
said. From what I understand, a bolt related to the selector shaft had
worked its way loose over time, allowing the shifting rods to move out
of place. I guess it couldn't get back into gear because the selector
was not aligned with the rods and was pushing uselessly against
something. They were able to access the "Shifting rods" above the gears
without dropping out the transmission, take out the springs (#16 from
http://www.realoem.com/bmw/showparts.do?model=1113&mospid=47309&btnr=23_0171&hg=
23&fg=15
) and put the selector back in place, fixed up the naughty bolt and
kept it in place with some  grippy paste stuff.

He also had the prior repair records, showing the clutch is only 3
years old, and didn't replace it, even though I had already conceded it
would be necessary. That's a class act for a shop.

I think it's a minor miracle, and also means that WB Motors is cleared
of any wrongdoing, as it seems like a slowly caused problem. Joe at WB
has always been very attentive and thorough, so I hope this post
doesn't hurt their business. Apparently it's a common problem for this
car, so I hope this thread can help someone else out.

Thanks!