Ken, Here's a pic before I staked it: This is it almost exactly a year ago from pretty close to the same camera angle but much closer up (you can tell how much the foliage has increased by the sheer # of leaves): There are two main leaders at this point, both suffering from the same top-heavy problem and leaning in the same direction. So I used two 6' plastic stakes about 2 feet away and twine+velcro straps to pull them upright and slightly separate them. How long do you think I should expect to leave it staked? I'd rather not do it for long if I can help it . . . just long enough for the branches to strengthen. It didn't have this problem last year but I'd say it has >3 times the foliage now. It's definitely a JM but I can't guarantee how true to bloodgood it will be. It grew up under a mature bloodgood at my dad's house, presumably from seed? Either way I'm expecting it to be large for a JM . . . its parent tree is probably 15' high with an 8-10" trunk, and is at least 15-20 years old. This one is in a spot where that size would be fine, so I'm not worried about its growth potential . . . I just don't want abnormally fast growth to keep it from being the beautiful tree it has the potential to be. Thanks again.

Contact your local office of the University of Connecticut USDA Cooperative Extension Service and have the horticulturist come out and look. While I've not heard the Emerald Ash Borer is in Connecticut that does not mean they aren't. These wee larva are devastating Ash trees in many areas of the country and are spreading out. Here is a link that might be useful: Emerald Ash Borer

How does the top look? That wound looks like it was from last year. The wood is weathered grey and the callus tissue has begun to heal over. Maybe a buck rub, maybe a frost crack..., in any case it looks nasty but if the top looks healthy it will probably eventually (after a few years) heal over. Do not apply any paint or pruning sealer or anything. If the top is showing signs of stress, such as branches dying back, I would probably just replace it, especially if it is a specimen tree in your yard.

Leave the tree & the hole be.