Well, the answer is...the slide release has a tail piece that trips the disconnector. When reassembled, the slide release is being depressed by contact with the action bar. Just a few thousandths too much, is enough to disconnect the trigger. (talk about a hair-trigger disconnector...just look at it hard and it shuts down!)
Solution seems to be carefully removing material at the contact points at both ends of the slide release. That re-established the free play needed at the disconnector end. I'm only talking about less than a hundredth of an inch here...when the action is opened, the tail piece swings that thing away like a barn door...so there's no loss of functionality.
The wonder to me is how it worked when it was so dirty and gummy in there!