Hi,
I have read the description here and would like an opportunity to examine the armature if the model you are referring to. I know you probably have some animations that you would like to remain so creating another rig may be out of the question. I have fixed problems with animations in blender before and you can confirm by checking my reviews. You can check my portfolio on my profile here; https://www.freelancer.com/u/aspwriter; for 3D models, animations and renders I have done on projects in the past three years. I look forward to hearing from you.