The spotty, mottled, small brown and yellow areas could be damage from spider mites, which are found on the back of the leaf and require a hand lens to see. Aphids do similar damage but are larger and easily seen on the back of the leaves. The dry summer we have had is ideal for high spider mite populations. Large trees typically recover well from both these insects when growing conditions are good.
The larger brown areas scattered here and there could be anthracnose.
Both of these conditions have only a few basic actions you can take yourself on large trees. First you can place a long soaker hose around the root zone and give the tree extra water. Try to get the root zone moistened at least 12 inches down. Thats a lot of water for these big trees! Second, keep the leaves raked up and removed from the property so as many overwintering pests and fungi as possible are removed.
As noted in your sycamore question/answer from last year, you may submit samples to MSU Lab, or consult an arborist. I would recommend an arborist visit since your trees have had issues over several years. An arborist can assess the whole environment, past years growth indicators, and give a specific diagnosis for this season's problems. He/she will give you a tree care plan to follow.
Here is the certified arborist web site- www.treesaregood.org
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