I'm having a difficult time figuring out what is going on with your cherry tree.* It could be more then one problem and pictures of the dead branches, places where the bark is missing or split and the spots on the leaves would be most helpful.* Cherry trees are plagued by many diseases and pests.
It almost sounds as if the older tree has been in decline for a while now.* That makes me wonder if there could be something going on with the root system.* A picture of the base of the tree would also be most helpful.* I'm wondering if there could be some girdling roots, especially if the declining limbs are located in one area.* Another possibility could be too much soil or mulch against the trunk, burying the rootflare.* If your tree looks like a telephone pole in the ground instead of having a flare at the base, that could cause the decline.* Take a look here at rootflare and too deeply planted trees to see if any of this looks famaliar.
Tree root and mulching info.
You may need to remove some soil and look at the roots.* Some of the symptoms you describe almost sound like verticillium wilt.* Does this look like what you see?
Any of this root rot sound famaliar?
Do you see any oozing of sap on the damaged limbs?* That would be bacterial canker.* I have my suspiciions this could be the problem.
Look at other cankers here, especially #3 for Valsa canker.
Fireblight isn't high on my list of possibilities, but it's worth looking at.
This is what cherry leaf spot looks like,
Cherry brown rot.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.