Don't know about autoboxes, but the two I have here have 236K and 262K miles on them - both manuals, and I've seen no evidence that the gearbox on either had ever been changed.
You could, of course, do yourself a favour and unless the one you are looking for is _really_ cheap and in very good condition, get a manual - you'll get more mpg and won't have to worry about when/if the box will expire. Of course, the manuals have their own expensive issues from time to time (somebody thought it'd be a great idea to fit them with a "dual mass flywheel", which I'm told is about £600 (+ labour) or something disgusting like that). But in 70K miles having driven one I've never had a transmission problem, which is more than I can say for the ZF auto box (I seem to remember it's the 4HP22 as fitted to the XJ40 Jaguar, but I could be wrong). Having said that, the slightly later 4HP24 box I've not managed to break yet, even though it's bolted to a 7.6 litre V12 engine in one of my other toys.
Clearly, YMMV.
