[A8] New Lister, Trans. Question

[urquattro at comcast.net]

Hi out there,
I know this list is pretty quiet and the Audiworld is the more active choice for A8 fodder, but I really much prefer the simple functionality of the audifans lists (urq lister since its inception) so I'll try this. 

Last winter, with a few extra bucks in hand, I purchased a (gasp) 163k mile '97 4.2q, very clean with exten$ive maintenance records and a few nice little upgrades. Car drove fabulously on the test drive; did not exhibit any suspicious tranny behavior. It has more or less been stored the last 7 months until I had some time to spend getting familiar with it. 

Today is the 3rd time I've driven it a longish distance and on the freeway I noticed the notorious torque converter "thump" for the first time. It seems to be even worse when the car is driven in "4". The tranny fluid/filter -were- changed some time back, but the more I read about these, the more I'm beginning to feel a bit nauseous about what I've gotten myself into. 

I would love some clarification on:

-how long between the beginnings of the "thump" and the complete demise of the tranny

-whether and how the "thump" itself actually leads to the aforementioned demise

-whether there is any warning before the transmission fails to the point the car is undriveable (ie could I limp a few hundred miles home or be completely stranded)

-has anyone bought a ZF-rebuilt trans, and if so, what kind of luck have they had with it; how much did it cost

I absolutely love driving the car; it's everything I've loved about my various 5kq's but SO much better. Considering the small money I paid for it; I might be able to live with a big hit up front to get a decent trans in it, but the picture on what that costs / whether that solves the problem in the long term is a bit fuzzy still.

Any discussion, annecdotal information greatly appreciated!
TIA,
Jon
'97 a8 4.2q
'95 90
'85 urq 20vt