Another item I forgot to mention was that the trans fluid was recently changed. Until I read some other posts, I was not aware of it's sensitivity to fluid level. Appears that it should be 10 mm under ADD when cold and never over full when hot. I will check this too.
I also flushed the radiator (and entire cooling system) due to PO having the dreaded "green" coolant and re-filled with the correct MB gold. Wondering if the wrong coolent may have contributed to a coolant obstruction that affect the trans circuit? Still need confirmation that there is an internal or external cooler.