This leaf has some maple bladder galls on it. These galls rarely threaten the health of an established tree and treatment is generally not necessary. Read here:
You say the tree shows signs of disease and distress. Write back with appropriate photos, including photos of the entire tree, if this tree has problems other than these galls.
The crack is probably a winter injury crack caused by sunscald. It has no doubt been on the tree for several years. I also see what looks like lichen or fungal growth on the trunk. This could indicate the tree may have rot inside that crack. You don't show the crown of the tree, but things to look for are dead branches and early leaf drop.
Here are some links:
I suggest you have a certified arborist check this tree out. The galls are not a problem, the lichen is probably not a problem, but if there is rotting in that frost crack, there could be a problem: