I treated the tree with a bayer systemic just to be sure, and plan to do get rid of the rotting wood and apply a sealant when i can get ahold of some to use.
Thank you for that information Shibui, it likely isn’t sunburn as it hasn’t been very hot lately, but I do live in southern Arizona and we experience very sunny days/hot afternoons (though my maples get shade passed noon).
I will see how things progress and hopefully no real damage is done other than some surface rotting.. which may end up not being so bad.
It’s such a vigorous tree though, I would be suprised if it became ill.