This seems to have some interesting/ pertinent elements, though in more pathological terms than may apply for you guys:
http://www.emedicine.com/ped/topic2646.htm
Oh, it won't let me copy and paste. Phooey. It seems like Mo might have some of the elements of disinhibited RAD, and that you guys being a secure attachment for him now is the best possible thing. (I mean duh, but.) The "Treatment" part at the bottom seems to indicate that you are doing exactly what you should be doing. The part starting with "sensitivity, or emotional availability" seems especially apropos.
Here's how to contact the sears website:
[email protected]
This page gives more details on process:
http://www.askdrsears.com/contact.asp
Finally, an unformed thought that I'm trying to form... will blather and see if it goes anywhere. Did you see the question from _heatwave_ about porn and her relationship with her husband? Nimh had a great response about porn being a red herring.
Mo's history is far from a red herring, he has an actual history that actually has to be taken into account and that no doubt actually affects him, nothing to be discounted by a long shot. But I worry that you are focusing on that to the extent of not letting your (truly stellar) instincts shine through. I'm worried that you're second-guessing yourself too much.
Parenting is just plain tough, and it's pleasanter to record the fun and sweet stuff for posterity, but that doesn't mean it's the whole story. My kid is jaw-droppingly frustrating often, (especially when she's been sick too much and home too much and we're both bored and getting on each others' nerves, grrr), and I can guess and follow my instincts but I can also see how easy it would be if there were some THING that could account for her more mysterious behavior to focus on that THING. But the fact is that even without a thing she has plenty of mysterious behavior.
Hmm, didn't quite get where I hoped to go.
Bottom line, I think you're doing a stupendous job, and I think one aspect of the stupendousness is your ability to open up and make yourself vulnerable, not just in the obvious ways but in so consciously examining your own parenting and your willingness to adjust if need be.