Sounds like vacuum line(s) to the doors leaked, and the leak has worsened. Some troubleshooting with a vacuum source (MityVac is highly recommended here, do a Search) will be in order.

The 85 SD should have an electrically operated vacuum pump in the trunk, by the spare, to make vacuum for the locks. Be sure it's running.

Does the key not turn in the trunk lock? I understand that the key will mechanically lock and unlock the trunk, as well as start the vacuum pump to pull the other locks open or closed.

Others will add to this I'm sure.

Best Regards,
Jim