That is a bummer about your shin issue. You did an awesome job detailing what has bothering you but I have some more clarifying questions, if you are game to answer them.
1. Is your aching and burning at mid shin to the inside or outside of the shin bone?
2. How large of size is the area? Does it run vertically along the shin?
3. Is the discomfort constant doesn’t change with activity, constant but changes with activity, or comes and goes?
4. Does the pain change through the day from morning to afternoon to evening?
5. What activities are more aggravating than others? What things are you doing that help it feel better
Other things I was wondering about? How is the style of shoe you are wearing now compared to when you were running at University (thinking about heel to toe drop)? How has your body changed since your time with peak mileage (body weight or other factors)?
Have you cycled or used the elliptical in the past? Or do these make your symptoms worse? These could be viable options to continue to get zone 1 training in. They may not be as optimal, but definitely better than training.
I haven’t really posted much on here. Just as a FYI I am a Doctor of Physical Therapy near Seattle and I just finished up reading Training For The New Alpinism