You were right--the spring was the trick--it slid right out. Thanks so much for your input! Maybe I could have eventually figured it out, but tips like this are invaluable. (I love this site)

I got out the cylinder before dawn this morning (up early, especially when there's a project weighing on my mind) but waited to post this message until now because I was hoping to report that it was all done and happily back together, but....no such luck!

One important and obvious point I learned--it's really important that everything is put back together EXACTLY as it came out. I missed something here and there and it made all the difference (it was helpful to have the other lock handle and mechanism intact to see how it was done). Also, although I tried to be as gentle as possible, it seems the tips of the spring are not gripping the inner (new) lock cylinder inside the casing as well as they did the old cylinder. I'm not sure if it's stretched a bit a tiny bit in the removal but I'm using some pliers to slightly bend its gripping ends more tightly. I think that's why the new lock cylinder still rolls around completely back and forth inside the casing when I turn the key.

Also, the other lock pin is jammed--still working on it. Ugh. May need to get a new set, but I haven't given up yet.

Will let you know of the progress and hopefully job successfully completed.

much thanks!

Holly