Bill- Yellowing of leaves can be just a natural aging process. My Maudiae types tend to keep their leaves for over two years before turning yellow and drop. My fairrieanum*Yosemite Moon hybrid is losing the oldest growth that flowered last spring. That grow is about three years old. There are still 4 new growth, two of which are sending up flower buds. woo hoo~~
About natural aging, the old leaves would first turn yellow, then starting from the tip, it turns dark brown and dry out completely.
Now, one of my paphs have yellowing leaves (the bottom leaves) that are turning yellow from the base instead of the leaf tip. It is odd, but it is not wet, no fowl smell, plus it is about to open three flowers in a few days, so I don't want to disturb it.
I hope it is fine.
Regarding roots, I will post a new thread soon. I think of all the orchids I have, paphs have quite strange look to their roots. They simply look rotted to me at a first glance. but they were perfectly fine!