With regard to the question of whether or not to change the PTU oil and what it looked like, when I changed mine at 100K (I put in a drain plug), it was disgusting looking - thick, gooey and black and nothing like what would have gone in. I changed it about 6 times in a 2 week period and once flushed it with tranny fluid as a cleaning agent to get more of the goo out. After that when I changed at about 15K intervals it is much cleaner than it was at the initial change and no issues with the PTU at 160K.
As far as whether or not is it necessary, a friend once said "it's cheaper to change oil than parts" and since the oil was as bad as it was, a PTU oil change is cheap insurance regardless of Ford's recommendation of it being a lifetime fill. It did last through the warranty period and that is Ford's concern. As many others have surmised, I also think that since it is so close to the exhaust, this of course doesn't help the oil life. What is the downside to a PTU oil change - $20 now that I have a drain and I do it myself.