Why does one red oak have pale leaves with brown spots?

We would have to see and possibly test the tree. It sounds like you may have a fungal problem, possibly below and above. I would first check to see if buttress roots are visible at the base of the tree. Then, check for girdling roots. If the tree has no visible root flare, then it may be decaying from beneath. It may also have phytopthora, a decay organism that root prunes the tree destroying root hairs and making absorption of nutrients difficult.