Are you looking for someone to fix a center diff or just open it up for you?
Leaving it in the car and trying to pull it apart on jackstands is not how that is done. Remove, tear down, inspect. If you pull it and bring to to my garage I don't mind opening it up for you. My garage is around the corner in Shrewsbury.
If you don't have the $400 to diagnose it, how are you going to get the money to actually remove, replace broken bits, and reinstall the parts? Don't mean that in a dickish way... this is probably the biggest service you'll ever do on that subaru. Start planning/budgeting accordingly! Sucks but that's the deal.