FYI in case it helps anyone else...

I have a 1996 2.4L Cavalier convertible with 150k miles. One day the automatic transmission started to have trouble shifting into 2nd gear. It would wind up to high RPM before shifting (probably to 3rd gear). I had never changed the transmission fluid. My trusted mechanic told me to take it to his (trusted) transmission shop. They rebuilt it for $2300 (here in expensive Silicon Valley) with a 1-year warranty. The transmission shop owner said that clutches (and band?) were worn out. He also said that (contrary to the owner's manual) I should change the transmission fluid every 2 years. (But if you haven't been changing it every 2 years, you shouldn't change it until it fails because it becomes dependent on the gritty fluid.)

Side note: He said that my manual-transmission 1996 Cavalier requires no transmission-fluid change and no maintenance until the clutch wears out.

I was willing to put $2300 into a 1996, 150k mile Cavalier because (1) it's a convertible (2) it's otherwise in good shape, (3) Cavaliers were so popular that there are lots of cheap aftermarket parts available for repairs, (4) it's cheap to insure, (5) sales tax is 9%, and (6) none of the car companies offer reasonably-priced, practical (FWD or AWD, reliable, true-5-seater-with-reasonable-trunk) convertibles.

FYI: My buddy had the transmission on his Audio A6 rebuilt at the same shop and it cost $5k. I'd love an Audi convertible but they have terrible reliability (especially their transmissions) and they are terribly expensive to repair.

WOW, that was crazy expensive!
You could have gotten a fully rebuilt one for not much over a grand. Including a 3 year warranty.
https://www.rockauto.com/en/moreinfo.php?pk=4762827&cc=1038293&jsn=567

Personally, I think it is a good idea to change the oil in a manual transmission every 30,000 miles or so. It is easy and cheap, even if you use the more expensive Amsoil synchromesh (great stuff, btw).

I had not changed the fluid in my 2001 2.2 until last April (17 years on the original fluid) because everything I ever saw said it "never" needed to be changed. Well for years my car had made the most outrageous rattling noise in lower gears and I decided - basically just out of curiosity - to drain what had been in there out and see what it looked like (and how much was in there of the 1.8 quart capacity). Well it looked pretty well-used and sort of a dark brown/red-wine color mix. I added 1.8 quarts last April and then 1 year later - last month, drained it all out because for the first 6 months after adding it last year - it leaked out like crazy from the hole where the starter/engine/trans meet). A total of .7 quarts came out so I had lost 1.1 quarts from the leak. And of course for the last month, every place I stop, I leave a big puddle of red fluid behind. So my car doesn't seem to care if there is much fluid or what the condition of the fluid is. It is nice to have a couple of months of quiet and no rattling though - before it gets down to the level where it is noisy as hell again.

Thanks Butch! I didn't think of buying a rebuilt tranny. If I had, I wonder how much it would have cost me to have the old one removed and the rebuilt one installed. I'd guess that the total cost may have been comparable. If there's a "next time", I'll look into that.