It is far easier to select a tree that will be adaptable to existing conditions than to attempt to permanently alter those conditions to accommodate the tree :-) Having said that, hard to find a 'small' tree that will work. Nyssa sylvatica (tupelo) is an excellent choice for poor drainage but will eventually exceed your height requirements. You could also try one of the smaller willows or coppice it annually to keep it small. Or train a redtwig dogwood into a tree form

You could go up instead of down, by dumping topsoil on top of the damp area and planting above the level of dampness.

If the maple has become infested with a destructive pathogen it may go on to decline and dwindle despite now being out of the unfavorable planting hole.

gardengal48-I like your idea of a redtwig dogwood. How big do these get? What color is their foliage? I think I have seen them around my area, but don't ever notice them except for in winter because of their bright red color. I might just do that instead of a tree if they get tall enough. Thanks!

They can get quite large - 8-10' if left unpruned, sometimes larger (for the native species, Cornus sericea). Had one of the natives in a previous garden that grew in quite a tree-like form that was easily 10' plus.

The natives have plain green foliage and are not particularly showy or very ornamental except for their red winter stems. I prefer the Tatarian dogwood, Cornus alba, which is available in a variety of variegated forms. Cornus alba 'Elegantissima' has a cream and green variegation that is very attractive, grows quite large and is available at most nurseries. You can also find shrub dogwoods with yellow twigs and again with variegated foliage if you like - Cornus sericea 'Silver and Gold' is a pretty stunning plant.