The slow walk, bent arm, and palilalia sure sound like primary symptoms that would fit together in some distinct way.
I agree, and those things can't be explained away as 'gifted quirkiness'. (
Or can they? LOL)
For visualizing mechanical systems, I was thinking along the lines of being able to describe the connections in a motor or to know that if one cog rotates one way, then another rotates another way. Basically internal mechanical aptitude contrasted to what vision or dexterity might limit outwardly.
I'm not sure how to answer that. If he knows how something works after having read about how it works, he can explain it well enough, but he's not great at walking up to something and figuring it out on the spot --at least I don't think so. Even when he builds and constructs things, which he likes to do, he doesn't use the best logic, imo. This is one area where I can clearly see that his mind works differently. It seems to me that he's more into the creative side of things than the functional side, though he does like to try to make things that work correctly. It just seems that he can't 'see' how to do that.
