Ceiling damage in Co-op apartment?

We live on the 2nd floor of a three story Co-op apartment complex in Chicago. We have suffered severe, ongoing water damage to our guest bathroom from the tenants above us. We own our unit, but they are renting the 3rd floor unit. Despite complaints to our Co-op board, pictures and videos of the worsening damage, city inspector visits, nothing has been resolved and now the ceiling is threatening to cave in due to the excessive dripping. The bathroom and adjacent walls will now have to be completely replaced.We have been in litigation since 1/2009. Part of the problem is that neither the Co-op nor the owner want to be responsible for the damage. Since the leaking originates somewhere in the 3rd floor, fixing our place will not solve the problem. (it has been dripping for 3 years!) We just feel so trapped. Is there any way we can expedite the process? How can we get out of this? We have an outstanding mortgage and the unit is in no shape to be sold. Should we get another lawyer?