May not be your problem but when my previous RV reached that age I started having problems with the jack motors. Cured by removing the motors and cleaning the commutator and brushes/brush rigging. What was happening on mine was 15 years of "brush dust" was causing the brushes to stick in their rigging and lose good contact with the motor's commutator, getting it burned and nasty. They would start running but any load/binding would just stop the motor. Some fine sandpaper fixed it along with cleaning brushes and brush holders. The first one I pulled the jack off to do it, once I knew how they went together, I was able to do the rest attached with a long socket extension to reach the motor mounting bolts.